Due to inclement weather conditions, the Institute will delay opening until 10am on March 4th, 2019.

LOCATION: COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20190304T173000Z DTEND:20190304T183000Z SUMMARY:Princeton University Princeton Gravity Initiative Lunch, "Analytic Black-Hole Binary Mergers: Waveforms and Kicks from First Principles" (Sean McWilliams, West Virginia University) DESCRIPTION:The group's website is:

In 1975 Hawking showed that the evaporation of black holes creates a problem for unitarity. This argument can be made rigorous through the small corrections theorem, and implies that there must be a fundamental change in our picture of semiclassical gravity. In string theory it appears that black hole microstates are horizon sized quantum objects called fuzzballs. We argue that virtual fuzzballs are an important component of the vacuum; their resistance to compression is needed to maintain causality in the semiclassical approximation. This component of the vacuum is also likely to be relevant to understanding cosmology.

There is a substantial effort in the physics community to search for dark matter interactions with the Standard Model of particle physics. Collisions between dark matter particles and baryons exchange heat and momentum in the early Universe, enabling a search for dark matter interactions using cosmological observations in a parameter space that is complementary to that of direct detection. In this talk, I will describe the effects of scattering in cosmology and show constraints using Planck 2015 data and SDSS-identified satellites. I will also discuss the implications of late-time scattering during the era of Cosmic Dawn.

**The Princeton Gravity Initiative** was founded to elevate local research exploring the mysteries of gravity across the disciplines of mathematics, physics and astrophysics. Our *inaugural conference* celebrates this theme, bringing together leading experts from nearby institutions, and highlighting the work of the next generation of young researchers at Princeton.Register here: https://goo.gl/forms/ILyPvlZbrq6wAY6j1

**The Princeton Gravity Initiative** was founded to elevate local research exploring the mysteries of gravity across the disciplines of mathematics, physics and astrophysics. Our *inaugural conference* celebrates this theme, bringing together leading experts from nearby institutions, and highlighting the work of the next generation of young researchers at Princeton.Register here: https://goo.gl/forms/ILyPvlZbrq6wAY6j1

**The Princeton Gravity Initiative** was founded to elevate local research exploring the mysteries of gravity across the disciplines of mathematics, physics and astrophysics. Our *inaugural conference* celebrates this theme, bringing together leading experts from nearby institutions, and highlighting the work of the next generation of young researchers at Princeton.Register here: https://goo.gl/forms/ILyPvlZbrq6wAY6j1

The group's website is:

Infinite-dimensional conformal symmetry in two dimensions equips 2d CFTs with an integrable structure - an infinite tower of quantum KdV charges in involution. I will discuss the role of this integrable structure in constraining thermalization and will show that 2d CFTs satisfy generalized eigenstate thermalization with the set of quantum KdV charges forming a complete set of thermodynamically relevant quantities. I will also review recent progress calculating the spectrum of qKdV charges and generalized partition function of 2d theories in the limit of large central charge.

Pulsars act as accurate clocks, sensitive to gravitational redshift and acceleration induced by transiting clumps of matter. We study the sensitivity of pulsar timing arrays (PTAs) to single transiting compact objects, focusing on primordial black holes and compact subhalos in the mass range from 10−12 Msun to well above 100 M sun. We find that the Square Kilometer Array can constrain such objects to be a subdominant component of the dark matter over this entire mass range, with sensitivity to a dark matter sub-component reaching the sub-percent level over significant parts of this range. We also find that PTAs offer an opportunity to probe substantially less dense objects than lensing because of the large effective radius over which such objects can be observed, and we quantify the subhalo concentration parameters which can be constrained.

Light scalar dark matter fields can exhibit several interesting aspects to their cosmological evolution. I will focus mostly on structure formation with ultralight axions and with the QCD axion. The standard scenario leads to a *suppression* of structure on small scales. I will show that there can also be an *enhancement *of power just below the scale of suppression. This effect will lead to the formation of compact axion halos, with broad implications for their observational prospects.**Reading list**

Cosmology reviews for:-- ultralight axions (Marsh): https://arxiv.org/abs/1510.07633

-- QCD axion (Wantz & Shellard): https://arxiv.org/abs/0910.1066

First mentions of the enhanced structure effect:

-- by Zhang & Chiueh https://arxiv.org/abs/1702.07065

-- by Cedeno et al https://arxiv.org/abs/1703.10180

Program Organizers: Tolya Dymarsky, Tom Faulkner, Xiaoliang Qi, Herman Verlinde The topics of non-equilibrium quantum physics and quantum chaotic dynamics are currently playing a central role in many areas of physics, from the attempt to understand quantum gravity in the bulk, to the emergence of anomalous transport in various condensed matter systems. The goal of the workshop is to address these questions from the point of view of conformal field theories, which provide a natural relevant theoretical framework. This conference will bring together a group of experts working on various aspects of CFTs ranging from the large central charge limit in two dimensions, to Eigenstate Thermalization Hypothesis, to higher-dimensional bootstrap at finite temperature, and beyond.

Time-reversal symmetry is one of fundamental symmetries that can present in many quantum mechanical systems. It plays an important role in many-body quantum systems, as demonstrated, for example, in the physics of topological insulators. In this talk, I will discuss topology and quantum entanglement protected and detected by time-reversal symmetry. Of particular importance for us is the so-called *partial transpose* -- a quantum information theoretical operation closely related to time-reversal. I will discuss how it can be used to detect topological properties of many-body ground state of topological insulators and superconductors without relying on single particle band structures, and, also, how it can be used to quantify quantum entanglement of mixed quantum states.

I will review the perturbative (genus) expansion of one-matrix integrals via the loop equations, and the streamlined version due to Eynard. I will review double-scaled matrix integrals and discuss a heuristic method for computing some nonperturbative effects. For a thorough modern discussion of the loop equations and the connection to "topological recursion," see

https://arxiv.org/abs/1510.04430

I will discuss the contribution of higher-genus surfaces in JT gravity. In work with Saad and Shenker, we use Mirzakhani's recursion and work of Eynard and Orantin to show that these contributions exactly coincide with the genus expansion of a particular double-scaled matrix integral. I will explain this and then discuss a JT gravity interpretation of nonperturbative effects in this matrix integral.

At the event horizon of a black hole, gravity reaches its most extreme behavior. Studying the dynamics of event horizons is key to understand gravity in the ultra-strong field regime and investigate the most fundamental properties of black holes. Black hole collisions provide a unique scenario to observe event horizons in a highly distorted and violently changing regime, which leads to a vast collection of phenomena that has not yet been detected by Advanced LIGO and Virgo. In this talk I will discuss the imprint that some of these phenomena leave in the gravitational-wave emission of black hole collisions and what it can teach us about the properties of black hole horizons. The group's website is:

Fractional quantum Hall (FQH) states are topologically ordered. Additionally, FQH states support a collective neutral excitation known as the Girvin-MacDonald-Platzman (GMP) mode. Certain features of this mode are independent of the microscopic details. The objective of the talk is to construct an effective theory includes both topological properties and the massive GMP mode. The theory reproduces the universal properties of chiral lowest Landau level (LLL) FQH states which lie beyond the TQFT data, such as the projected static structure factor and the GMP algebra of area-preserving diffeomorphisms. The dynamics of the mode is described by a fluctuating rank-2 symmetric, positive-definite tensor, which leads to a natural geometric (or gravitational) interpretation of the GMP mode.

Every CFT in dimensions greater than two contains an infinite set of Regge trajectories of local operators which, at large spin, asymptote to "double-twist" composites with vanishing anomalous dimension. In two dimensions, due to the existence of local conformal symmetry, this and other central results of the conformal bootstrap do not apply. In this talk I will discuss the incorporation of stress tensor dynamics into the CFT_2 analytic bootstrap and the non-perturbative implications for the dynamics and spectrum of AdS_3 quantum gravity, including an exact formula for the gravitational binding energy of multi-particle bound states at finite Newton's constant.

Motivated by an apparent counterexample to the Weak Gravity Conjecture, I will describe the difference between black hole extremality bounds and BPS bounds and (relatedly) the difference between superextremal particles and self-repulsive particles. This will lead us to some novel connections between BPS state counting, Calabi-Yau geometry, supergravity, black holes, and several Swampland conjectures.

In the Standard Model the Higgs boson is a very narrow resonance and therefore measuring its width is challenging. How can we constrain the Higgs boson total width at the LHC? Presently, the best limits on the Higgs boson total width at the LHC are set using the off-shell Higgs production and decay to ZZ in the four-lepton or two-lepton-two-neutrino final state and decay to WW in the two-lepton-two-neutrino final state. A review of all measurements performed by the ATLAS collaboration with Run 1 data and Run 2 data collected in 2015 and 2016 is presented. In the Standard Model the Higgs boson is a very narrow resonance and therefore measuring its width is challenging. How can we constrain the Higgs boson total width at the LHC? Presently, the best limits on the Higgs boson total width at the LHC are set using the off-shell Higgs production and decay to ZZ in the four-lepton or two-lepton-two-neutrino final state and decay to WW in the two-lepton-two-neutrino final state.A review of all measurements performed by the ATLAS collaboration with Run 1 data and Run 2 data collected in 2015 and 2016 is presented.

In this talk we revisit the holographic calculation of 1/2-BPS four-point functions from IIB supergravity compactified on $AdS_3\times S^3\times K3$. I will present evidence that the four-point functions exhibit a hidden 6d conformal symmetry. Using this hidden symmetry, we conjecture a general formula for all 1/2-BPS four-point functions of different conformal dimensions. We also develop a bootstrap-like algorithm to directly compute the correlators and check this proposal. Our method simplifies the traditional approach by exploiting the superconformal symmetry and eschews the knowledge of the (unknown) supergravity effective quartic vertices. We find the supergravity calculations are in perfect agreement with our conjecture.

I will describe a large ensemble of compactifications of type IIB string theory on Calabi-Yau threefold hypersurfaces, obtained by triangulating polytopes from the Kreuzer-Skarke list. We have developed methods to compute effective theories in the previously-inaccessible region with many Kahler moduli that plausibly contains almost all vacua in this class. We find that ultralight axions are ubiquitous when the sigma model expansion is under control. I will comment on work in progress examining the implications for axion inflation, axion dark matter, and astrophysical and cosmological axion searches. Finally, I will describe a related issue concerning the axion potential from non-BPS Euclidean D3-branes wrapping non-effective divisors, and will link this to geometric measure theory and the Weak Gravity Conjecture.

It is commonly believed that the NSR formalism has limitations in describing type II strings in RR background. In this talk, I discuss how we can systematically describe RR flux backgrounds in the framework of closed superstring field theory based on the NSR formalism, and present two applications of the framework: the pp-wave background supported by 5-form flux and $AdS_3\times S^3\times M_4$ supported by mixed 3-form fluxes.

I discuss ways in which we might make very precise measurements of the dark matter in the Milky Way using kinematic and composition data on stars from the ESA Gaia Mission and spectroscopic surveys like SDSS-IV and -V. I will show two methods that outperform traditional methods (eg, using the Jeans equations), one of which doesn’t even require the assumption of stationary or equilibrium. All methods require strong assumptions, however; there are no model-free ways to measure a truly non-interacting dark sector.

Massive black holes weighing from a few tens of thousands to tens of billions of solar masses inhabit the centers of today’s galaxies, including our own Milky Way. Massive black holes also shone as quasars in the past, with the earliest detected a mere billion years after the Big Bang. Along cosmic time, encounters between galaxies hosting massive black holes in their centers are expected to have produced binary massive black holes that eventually coalesced by emission of gravitational waves. I will discuss the physical processes through which massive black holes pair and bind, and how we can use gravitational wave observations with ESA’s planned satellite LISA to constrain the evolving population of massive black holes.

Charge transport near quantum critical points partly occur in phases with spontaneously broken symmetries. In an effective field theory approach, this transport can be described in a hydrodynamic theory with Goldstone modes encoding the broken symmetries. The symmetry can be restored gradually, modelling properties in the quantum critical region. I will discuss the case of broken translations (fluctuating stripes), partly in the presence of a high magnetic field (magnetophonons).

I will start by reviewing the three inequivalent topological twists of N = 4 SYM on arbitrary four-manifolds and briefly discuss the resulting topological QFTs. I will emphasise the role played by global anomalies of N = 4 in our story and the relation to anomalies in the TQFTs. I will then construct type IIB supergravity solutions that are holographic duals to the aforementioned twists. The supergravity solutions include a parameter dual to the omega deformation of Nekrasov. I will conclude by focussing on the omega deformation of flat space which is dual to a mild deformation of $AdS_5 x S^5$ preserving 24 supercharges.

Detecting light dark matter that interacts weakly with electromagnetism has recently become one of the benchmark goals of near-term and futuristic direct detection experiments. In this talk, I will discuss an alternative approach to directly detecting such models below the GeV-scale, leveraging on the recent interest and advances in resonant detectors, such as superconducting radiofrequency cavities and LC circuits.

**Speakers**: **Oscar Campos Dias**, University of Southampton, **Mihalis Dafermos**, Princeton; **Frederick Denef**, Columbia; **Isabel Garcia Garcia**, UCSB;** Daniel Harlow** (to be confirmed)**, **MIT;** Gary Horowitz**, UCSB; **Jonathan** **Luk**, Stanford; **Hirosi Ooguri**, CALTECH; **Matt Reece**, Harvard; **Tom Rudelius**, IAS; **Timm Wrase**, ITP. **Program Organizers**: Herman Verlinde and Netta Engelhardt **This workshop is being co-hosted by PCTS.**Please visit website to register.

**Speakers**: **Oscar Campos Dias**, University of Southampton, **Mihalis Dafermos**, Princeton; **Frederick Denef**, Columbia; **Isabel Garcia Garcia**, UCSB;** Daniel Harlow** (to be confirmed)**, **MIT;** Gary Horowitz**, UCSB; **Jonathan** **Luk**, Stanford; **Hirosi Ooguri**, CALTECH; **Matt Reece**, Harvard; **Tom Rudelius**, IAS; **Timm Wrase**, ITP. **Program Organizers**: Herman Verlinde and Netta Engelhardt **This workshop is being co-hosted by PCTS.**Please visit website to register.

Superstring theory is our best candidate for the ultimate unification of general relativity and quantum mechanics. Although predictions of the theory are typically at extremely high energy and out of reach of current experiments and observations, several non-trivial constraints on its low energy effective theory have been found. Because of the unusual ultraviolet behavior of gravitational theory, the standard argument for separation of scales may not work for gravity, leading to robust low energy predictions of consistency requirements at high energy. In this colloquium talk, I will start by explaining why the unification of general relativity and quantum mechanics has been difficult. After introducing the holographic principle as our guide to the unification, I will discuss its use in finding constraints on symmetry in quantum gravity. I will also discuss other conjectures on low energy effective theories, collectively called swampland conditions, with various levels of rigors. They include the weak gravity conjecture, which gives a lower bound on Coulomb-type forces relative to the gravitational force, and the distance conjecture, which is about structure of the space of scalar fields. I will discuss consequences of the conjectures.

What is the Dark Matter which makes 85% of the matter in the Universe? We have been asking this question for many decades and used a variety of experimental approaches to address it, with detectors on Earth and in space. Yet, the nature of Dark Matter remains a mystery. An answer to this fundamental question will likely come from ongoing and future searches with accelerators, indirect and direct detection. Detection of a Dark Matter signal in an ultra-low background terrestrial detector will provide the most direct evidence of its existence and will represent a ground-breaking discovery in physics and cosmology. Among the variety of dark matter detectors, liquid xenon time projection chambers have shown to be the most sensitive, thanks to a combination of very large target mass, ultra-low background and excellent signal-to-noise discrimination. Experiments based on this technology have led the field for the past decade. I will focus on the XENON project and its prospects to continue to be at the forefront of dark matter direct detection in the coming decade.

**Speakers**: **Oscar Campos Dias**, University of Southampton, **Mihalis Dafermos**, Princeton; **Frederick Denef**, Columbia; **Isabel Garcia Garcia**, UCSB;** Daniel Harlow** (to be confirmed)**, **MIT;** Gary Horowitz**, UCSB; **Jonathan** **Luk**, Stanford; **Hirosi Ooguri**, CALTECH; **Matt Reece**, Harvard; **Tom Rudelius**, IAS; **Timm Wrase**, ITP. **Program Organizers**: Herman Verlinde and Netta Engelhardt **This workshop is being co-hosted by PCTS.**Please visit website to register.

In many-body chaotic systems, the size of an operator generically grows in Heisenberg evolution, and is measured by out-of-time-ordered four-point functions. However, these only provide a coarse probe of the full underlying operator growth structure. We develop a methodology to derive the full growth structure of fermionic systems, that also naturally introduces the effect of finite temperature. We then apply our methodology to the SYK model, which features all-to-all q-body interactions. We derive the full operator growth structure in the large q limit at all temperatures. We see that its temperature dependence has a remarkably simple form consistent with the slowing down of scrambling as temperature is decreased. Furthermore, the finite-temperature scrambling follows a modified epidemic model, where the thermal state serves as a vaccinated population, thereby slowing the overall rate of infection. Finally and perhaps most interestingly, we note that at strong coupling/low temperatures the cascade into larger operators mirrors an AdS2-Rindler probe particle's growth into states of larger global energy or null momentum.

The observed flattening of rotation curves is usually considered strong evidence for the existence of dark matter on galactic scales. However, observations such as the Baryonic Tully-Fisher Relation and the Radial Acceleration Relation suggest that the observed dynamics in galaxies are strongly correlated with the distribution of baryonic matter. This is challenging to explain in the context of dark matter, motivating low-acceleration modifications to gravity as an alternative to the dark matter hypothesis. I will present a framework to test a general class of modifications to gravity using local Milky Way observables that probe both the radial and vertical components of the galactic acceleration. For concreteness, I will focus on Modified Newtonian Dynamics (MOND), a modification to gravity that increases the magnitude but does not change the direction of the gravitational acceleration. I will show that a modification to gravity of this type is in tension with observations of the Milky Way's baryonic profile and that a spherical dark matter halo provides a better fit to the data. I may also discuss current work extending this analysis to other theories such superfluid dark matter.

Crystalline biominerals cost energy but provide the organism making them provide with skeletal support, locomotion, biting and mastication, carnivory, gravity and magnetic field sensing, and many others. How these crystals are formed is intensely studied because it is a widespread natural phenomenon, but also because it can teach us new synthesis strategies to produced targeted materials. I will discuss two key mechanisms:1. Crystallization by particle attachment in diverse marine organisms2. A new toughening mechanism first discovered in molecular dynamics simulations, then observed in human teeth.

My talk will aim to be a friendly introduction for condensed matter friends, mathematicians, and QFT theorists alike --- I shall quickly review and warm up the use of higher symmetries and anomalies of gauge theories and condensed matter systems. Then I will present the results of recent work [arXiv:1904.00994].We explore 4d time-reversal symmetric pure Yang-Mills (YM) gauge theories of an SU(2) gauge group with a second-Chern-class topological term at $\theta=\pi (SU(2) \theta=\pi YM)$ living as boundary conditions of 5d topological state (5d bordism invariants of mod 2 class, or 5d higher-1-form-center-symmetry-protected interacting (SPT) "topological superconductor" in condensed matter). We find their "Fantastic Four Siblings" with four sets of new higher "anomalies" associated with the Kramers singlet/doublet and bosonic/fermionic properties of Wilson lines. Via Weyl's gauge principle, by dynamically gauging the 1-form center symmetry, we transform a 5d bulk SPTs into a symmetry-enriched topologically ordered state (SETs) as 5d higher-gauge TQFT. Apply the tool introduced in [arXiv:1612.09298], we derive new exotic anyonic statistics of extended objects such as 2-worldsheet of strings and 3-worldvolume of branes, which physically characterize the 5d SETs. We discover new triple and quadruple link invariants potentially associated with the underlying 5d TQFTs, hinting an intrinsic relation between non-supersymmetric 4d pure YM and topological links in 5d. We provide lattice simplicial complex and "condensed matter" regularizations and then comment on 4d gauge dynamics.

I will discuss new universal bounds on the spectra of two-dimensional unitary, compact conformal field theories coming from the modular bootstrap. In the presence of a twist gap amongst the Virasoro primary operators (where twist is defined as the difference between total conformal dimension and spin), I will show that there is a universal expression for the density of states that extends beyond the usual Cardy regime. I will also describe a new upper bound on the lowest twist primary operator present in any CFT. For theories holographically dual to large-radius gravity in $AdS_3$, this new bound is below the BTZ threshold, which implies that states that cannot be described as BTZ black holes must exist.

It has been recently pointed out that variable weak gravitational lensing effects on the motion of background stars can be used to probe nonluminous structures inside the Milky Way halo. I will describe one possible detection strategy targeting collapsed dark matter structures in the mass range from million to billion solar masses. The data analysis technique will be discussed in detail with an application to Gaia's second data release.

The LIGO/VIRGO collaboration has just started their observing run 3. I will first give an introduction to gravitational wave searches and the events that have been found so far and describe some of the interesting astrophysics problems that might be addressed in the coming few years. Together with the rest of the IAS team, I will then describe the results of the searches for new events in the publicly available LIGO data that we have carried out (https://arxiv.org/pdf/1902.10331.pdf, https://arxiv.org/pdf/1904.07214.pdf, https://arxiv.org/pdf/1902.10341.pdf). These searches have nearly doubled the catalog of binary black hole mergers.

Understanding strongly interacting quantum many-body systems is one of the central challenges of condensed matter physics. The strong correlations of interacting quantum systems can lead to incredibly rich phase diagrams, and various intertwined or competing orders. The goal of this workshop is to bring together experimental and theoretical experts to synthesize the recent developments in interacting condensed matter systems, and to forge the future directions of the field. Several highlighted topics of the workshop include (but not limited to): superconductivity and correlated insulating phases in twisted bilayer graphene and other Moire systems, topological and interacting states in partially occupied Landau levels, and recent progress in the studies of high-temperature superconductors.**This workshop is co-sponsored by the Department of Physics and PCCM and the Gordon and Betty Moore Foundation.****This conference will be live streamed and can be viewed at this ****link**.

The collective inspirals of very close-separation supermassive black holes (SMBHs) are expected to produce a stochastic gravitational wave background (GWB) at nHz frequencies, which is accessible to pulsar timing arrays. However, we have yet to detect this background or find any SMBH binaries that are sufficiently massive or at small enough separations to contribute appreciably to the GWB. Using Hubble Space Telescope imaging, we have identified a pair of rapidly-growing supermassive black holes (M>4.e8 solar masses) at z=0.2 that are separated by only 400 parsecs. While this pair is not currently in the GW-emission regime, it points to a population of SMBH pairs that should have merged by today, unless there is a final parsec problem. Using estimates for the number density of such sources, we place limits on the expected GWB amplitude. I'll discuss the issues surrounding these calculations and how we can expect to learn more about the GWB and SMBH dynamics as we search for more of these SMBH pairs.Lunch will be available outside the auditorium starting at 12pm on Thursday. If you would prefer to eat during the talk, you are welcome to do so, but we ask that you clean up after yourselves even more carefully than you normally would, the Physics colloquium happening in this same room a few hours later.Lunch will be catered by IQuisine; sign up for it by 12 pm Wednesday here:

**This workshop is co-sponsored by the Department of Physics and PCCM and the Gordon and Betty Moore Foundation.****This conference will be live streamed and can be viewed at this ****link**.

Anomalies are invariants under renormalization group flow which lead to powerful constraints on the phases of quantum field theories. I will explain how these ideas can be generalized to families of theories labelled by coupling constants like the theta angle in gauge theory. Using these ideas we will be able to prove that certain systems, such as Yang-Mills theory in 4d, necessarily have a phase transition as these parameters are varied. We will also show how to use the same ideas to constrain the dynamics of defects where coupling constants vary in spacetime.

**This workshop is co-sponsored by the Department of Physics and PCCM and the Gordon and Betty Moore Foundation.****This conference will be live streamed and can be viewed at this ****link**.

**This conference will be live streamed and can be viewed at this ****link**.

We present recent advances in constructions of globally consistent

F-theory compactifications with the exact chiral spectrum of the minimal

supersymmetric Standard Model. We highlight the first such example and

then turn to a subsequent systematic exploration of the landscape of

F-theory three-family Standard Models with a gauge coupling unification.

Employing algebraic geometry techniques, all global consistency

conditions of these models can be reduced to a single criterion on the

base of the underlying elliptically fibered Calabi-Yau fourfolds. For

toric bases, this criterion only depends on an associated polytope and

is satisfied for at least quadrillion bases, each of which defines a

distinct compactification. We conclude with pointing out important

outstanding issues.

The most pressing fine-tuning puzzles of the Standard Model — the cosmological constant and weak hierarchy problems, as well as the Higgs metastability — can all be understood as problems of near criticality. I will present a natural selection mechanism based on search optimization on the string landscape. The working assumption is that cosmological evolution on the multiverse has occurred for a finite time, much shorter than the exponentially-long global mixing time for the landscape. I will argue this imposes a strong selection pressure among hospitable vacua, favoring those that lie in optimal regions where the search algorithm is efficient. This satisfies the basic requirements for natural selection: a diverse gene pool, offered ab initio by the landscape; vacuum replication through cosmological expansion; and competition for a finite resource, namely the fraction of comoving volume. Optimality is defined by two competing requirements: search efficiency, which requires minimizing the mean-first passage time, and sweeping exploration, which requires recurrent random walks. Optimal landscape regions reach a compromise by lying at the critical boundary between recurrence and transience, thereby realizing the idea of self-organized criticality. The framework makes concrete phenomenological predictions: 1. The expected lifetime of our universe is ~10^{130} years, consistent with current Standard Model metastability estimates; 2. The SUSY breaking scale should be nearly Planckian; and 3. The predicted cosmological constant is M_Pl^4/N, which can account for the inferred vacuum energy if our optimal region contains N ~10^{120} vacua. Importantly, these predictions do not rely on anthropic reasoning and instead follow readily from optimality.

Cosmological hypotheses and oracular dreams of grandly unifying all the forces of nature foretold: neutrinos might weigh a tiny bit, those elusive particles might blow up stars, and the protons (and your ashes) would transform into light in $10^29$ years. Indeed, that man can live to 100, without the radioactivity in his bones killing him, proves that nucleons survive for at least $10^26$ years…far longer than the big-bang light in the sky which dates our universe to a mere $10^10$ years. Testing the unification theories demanded new technologies to search for ultra-rare interactions. The pioneering experiment would need fast, isochronous, single photoelectron light sensors; a $N_2$ calibration laser; reverse osmosis water; and fast, inexpensive waveform digitizers…ushering in an era of massive, totally-active, Cherenkov ring-imaging calorimeters. Successive detectors morphed the target medium of the initial detector (ultrapure water) into heavy water, seawater, solid water, and even clear and scintillating oil. The two neutrino sources for the seminal experiment -- the atmosphere and Supernova 1987a -- evolved to include near and far accelerators, our sun, and nuclear reactors.I will relate the demise of the simplest unifying theory while tracing the tortuous path from a deficit of atmospheric neutrinos to a definitive observation of neutrino oscillation…now enabling ambitious dreams of tomorrow: untangling the mystery of CP violation and hypothesizing the lepto-genesis of the cosmos.This lecture is dedicated to the memory of physicist Val Fitch, Princeton inventor of an early water Cherenkov counter and unraveler of CP invariance.Twitter: #PrincetonPhyColloq

The Advanced LIGO and VIRGO observatories detected several gravitational-wave events in their first and second observing runs from 2015 to 2017. The detections were only possible due to sophisticated analyses of noisy strain data that were historically conducted within the collaboration. Recently, we developed an entirely independent analysis of LIGO data that improved its reach by rigorously accounting for inherent systematics, and thereby identified seven new binary black-hole mergers within, including the highest spinning event reported to date. In this talk, I will provide a birds-eye view of the process used to make these detections.

Critical points of classical second-order phase transitions are thermodynamic phenomena of particular interest, driven by thermal fluctuations and characterized by emergent scale invariance and universal power-law correlations. At zero temperature quantum fluctuations can similarly drive sharp phase transitions between qualitatively distinct many-body ground states, but can potentially produce a richer phenomenology than at classical phase transitions due to intrinsically quantum effects such as quantum statistics, interference, and entanglement. A key problem in the field of quantum criticality is to understand the nature of quantum phase transitions in systems of interacting itinerant fermions, motivated by experiments on a variety of strongly correlated materials. In particular, much attention has been paid in recent years to materials in which itinerant fermions acquire a pseudo-relativistic Dirac dispersion, such as topological insulators and semimetals and certain spin liquids. In this talk I will discuss the rich phenomenology of quantum phase transitions in systems of two-dimensional Dirac fermions, which includes non-Fermi liquid behavior, emergent supersymmetry, finite-randomness quantum critical points in the presence of quenched disorder, and deconfined quantum criticality.

The properties of the smallest gravitationally-bound dark matter structures can be affected by non-trivial particle physics within the dark sector, and thus could provide the first hints of the non-gravitational interactions of dark matter. As our knowledge of Galactic stellar kinematics grows, we are discovering streams and debris consistent with tidally disruptions of this small-scale substructure. As these objects are no longer self-bound, new techniques are required to extract the properties of their progenitors. I will show that the conservation of phase space density and volume during the tidal disruption may provide the necessary handle to reconstruct the mass and density profile of the original substructure. Measuring the phase space density in real data constitutes a significant challenge, but I will demonstrate that several major sources of error can be dealt with in Gaia data.

Approximating high-dimensional functionals with low-dimensional models is a central issue of machine learning and physics. This talk shows deep convolutional neural network architectures take advantage of scale separation, symmetries and sparse representations. We introduce simplified architectures which can be analyzed mathematically. Scale separations is performed with wavelets and scale interactions are captured through phase coherence. We show applications to modeling of astrophysical turbulences, regression of quantum molecular energies as well as image classification and generation.

The Milky Way halo is the brightest source of dark matter (DM) annihilation on the sky. Indeed, the strength of the Galactic dark matter signal can be greater than that expected from dwarf galaxies even in regions away from the Inner Galaxy. In this talk, I will demonstrate the promise of the Milky Way halo, until now less focused on in the literature, as a DM annihilation target. I will describe some of the intricacies associated with searching for an annihilation signal in a large-scale object such as the Milky Way halo. Finally, I will show the results of searching for this signal in Fermi gamma-ray data, producing some of the strongest bounds on DM annihilation to-date. I will conclude by describing the implications of these results for the DM interpretation of the Galactic Center excess.

Our Universe is filled with Cosmic Microwave Background (CMB) radiation having an almost perfect black body spectrum with a temperature of To=2.7K. The number density of photons in our Universe exceeds the number density of electrons by a factor of more than a billion. In the expanding Universe the temperature at early times was higher than today: Tr = To (1+z), where z is the redshift.

Hydrogen recombination at redshifts z ~ 1100 - 1300 leads to a rapid decrease in the Thompson scattering optical depth of the Universe. When this optical depth becomes close to or lower than unity, the mean free path of the photons starts to exceed the horizon (~ ct) and they can reach us directly carrying information about the inhomogeneities in distribution of the density of matter, the gravitational potential and the velocities of electrons at that time. The WMAP and PLANCK spacecrafts have measured, with enormous accuracy, the traces of these inhomogeneities in the angular distribution of CMB, originating during the epoch of hydrogen recombination due to existence of the last scattering surface. The width of this surface is defined by the rate of two photon decay of 2s level of hydrogen atom and the escape of the Ly-alpha photons in the distant low frequency wing of this line due to the expansion of the Universe. The epoch of hydrogen recombination in the Universe defines the properties of the observed angular anisotropy and E-mode polarization of the CMB and leads to tiny distortions of the CMB spectrum from the black body spectrum.

There is an obvious question: "How and at which redshifts the observed, practically ideal, black body spectrum of Cosmic Microwave Background Radiation was created?"

I plan to describe the nature of the black body photosphere of the Universe and demonstrate why the production of low frequency photons due to the double Compton effect and their redistribution over a broad energy range due to Comptonization allows creation of an ideal black body spectrum at redshifts higher than z~ 2 $10^6$. This explains why we will never observe, in the spectrum of CMB, the traces of the giant energy release connected with the annihilation of positrons and electrons at redshifts z ~ $10^9$.

Nevertheless, **spectral features in the CMB energy spectrum** contain a wealth of information about the physical processes in the early Universe at redshifts below 2 x $10^6$. The CMB spectral distortions are complementary to all other probes of cosmology. In fact, most of the information contained in the CMB spectrum is inaccessible by any other means. Among the unavoidable reasons for the existence of the spectral distortions are: emission of the hydrogen line photons during cosmological recombination, energy release due to Silk damping of small scale sound waves and heating of primordial gas during the epoch of reionization. In addition scientists are looking for the CMB spectral distortions arising, for example, due to decay of unknown elementary particles with lifetime significantly shorter than the lifetime of our Universe or due to the evaporation of small mass primordial black holes.

Black holes allow a unique probe of spacetime in the strong-curvature regime. With the Event Horizon Telescope capturing humanities first image of a black hole, and the beginning of the era of gravitational-wave astronomy, an unprecedented wealth of data allows testing General Relativity in these most extreme conditions. To do so, it is crucial to have consistent and theoretically well-motivated theories to predict possible deviations. I will discuss theoretical progress in predicting generic modifications expected from quantum gravity. For static black holes, this includes the modified horizon structure and the resulting black-hole shadow. I will explicitly discuss modifications to the shadow shape and size of spinning and non-spinning black holes expected from asymptotically safe quantum gravity. Such effects could be a generic consequence of a larger class of quantum-gravity theories which exert a quantum repulsive force to resolve singularities.Further, I will discuss first results on the dynamics of black holes including higher-order curvature corrections. The latter are generically predicted by many quantum-gravity theories and only very weakly constrained by solar-system observations. I will present first results on a research program to numerically evolve dynamical black-hole spacetimes in quadratic gravity.

Hydrodynamics has been recently reformulated as an effective field theory based on an underlying Schwinger-Keldysh partition function. After an introduction to the formalism, I will show how effective actions of this type can be derived from holography using a mixed signature bulk spacetime whereby an eternal asymptotically anti-de Sitter black hole is glued to its Euclidean counterpart along an initial time slice in a way to match the desired double-time contour of the dual field theory. For concreteness, I will consider the example of dissipative low-energy dynamics of relativistic charged matter at strong coupling in a fixed thermal background.

We are experimentally investigating possible violations of the Pauli Exclusion Principle in the cosmic silence of the Gran Sasso underground laboratory in Italy, by hunting "impossible" atomic transitions. I shall present our recent results and method to hunt for small violations of the Pauli Exclusion Principle (PEP) for electrons through the search for PEP "prohibited" X-ray transitions in copper and lead targets within the VIP2 experiment, and discuss possible implications for theories beyond the Standard Model and our future plans.

We consider supersymmetric $AdS_3\times Y_7$ solutions of type IIB supergravity dual to N=(0,2) SCFTs in d=2, as well as $AdS_2\times Y_9$ solutions of D=11 supergravity dual to N=2 supersymmetric quantum mechanics, some of which arise as the near horizon limit of supersymmetric, charged black hole solutions in $AdS_4$. The geometry underlying these solutions was first identified in 2005-2007. Around that time infinite classes of explicit supergravity solutions were also found but, surprisingly, there was little progress in identifying the dual SCFTs.We will discuss new results concerning the $Y_{2n+1}$ geometries that provide significant new insights. For the case of $Y_7$, there is a novel variation principle that allows one to calculate the central charge of the dual SCFT without knowing the explicit metric. This provides a geometric dual of c-extremization for d=2 N=(0,2) SCFTs analogous to the well known geometric duals of a-maximization of d=4 N=1 SCFTs and F-extremization of d=3 N=2 SCFTs in the context of Sasaki-Einstein geometry. In the case of $Y_9$ the variational principle can also be used to obtain properties of the dual N=2 quantum mechanics as well as the entropy of a class of supersymmetric black holes in $AdS_4$ thus providing a geometric dual of $I$-extremization. We have also developed some powerful new tools based on a novel kind of toric geometry, which lead to additional insights as well as the prospect of making further significant progress in this area.

We are experimentally investigating possible violations of standard quantum mechanics’ predictions in the Gran Sasso underground laboratory in Italy. In particular, we are testing the collapse models, proposed as a solution of the “measurement problem” (Schroedinger’ cat paradox), by chasing the spontaneous radiation predicted by these models in the cosmic silence. I shall present our recent results on hunting this spontaneously emitted radiation, which set very stringent limits on models parameters. I shall also discuss the implications of our results and future plans.

I will discuss recent work that studies the evolution of the von Neumann entropy of a holographic boundary system dual to an evaporating black hole in AdS. This entropy is computed via the Engelhardt-Wall prescription of extremizing the generalized entropy functional, which is given by the sum of the area of a surface homologous to the boundary and the entropy of bulk matter on any spacelike region bounded by this homologous surface and the boundary. I'll present the surprising result of how this prescription, applied purely within the semiclassical approximation, correctly reproduces expected features of unitary black hole evaporation, such as the Page curve. I'll also discuss how the Hayden-Preskill protocol is realized, and share some thoughts on possible resolutions of the information and firewall paradoxes.Refs:

Section 4.3 of https://arxiv.org/abs/1810.02055

https://arxiv.org/abs/1905.08762

https://arxiv.org/abs/1905.08255

I shall present a series of frontier experiments searching for X rays coming from exotic atoms produced at the DAFNE collider of LNF-INFN (Italy) and from processes violating Quantum Mechanics’ predictions at the Italian Gran Sasso underground laboratory. In the first part of the talk I shall introduce the studies of kaonic atoms in the framework of the SIDDHARTA collaboration at the DAFNE Collider at the LNF-INFN, Frascati (Roma) laboratory. Combining the excellent quality kaon beam delivered by the DAFNE collider with new experimental techniques, as fast and very precise X ray detectors, like the Silicon Drift Detectors, we have performed unprecedented measurements on kaonic hydrogen and helium. Presently, a major upgrade of the setup, SIDDHARTA-2 is being realized to perform in the coming year the first ever measurement of kaonic deuterium. Kaonic atoms studies represent an opportunity to unlock the secrets of the strong interaction in the strangeness sector and understand the role of strangeness in the Universe, from nuclei to the stars. In the second part of the talk I shall present the VIP experiment at the LNGS underground laboratory searching for “impossible atoms”, i.e. atoms prohibited by the Pauli Exclusion principle, which might exist in some theories beyond the Standard Model. Also, I shall briefly discuss the search of the so-called spontaneous radiation linked with collapse models dealing with the “measurement problem” (Schroedinger’ cat paradox) and the interplay with gravity.

The AdS/CFT correspondence conjectures a duality between a theory of quantum gravity in Anti de Sitter space and a conformal field theory. Susskind identified an interesting paradox in this correspondence: namely some aspects of the behavior of eternal black holes, which partition space-time into two distinct regions connected by a “wormhole”, do not have an obvious CFT analogue. The conundrum is that the volume of the wormhole grows for a very long time, whereas in the dual space the CFT dynamics of most black hole systems are conjectured to be “scrambling” --- the expectation values of local operators saturate very quickly to their equilibrium values. What quantity in the CFT could possibly then be dual to the wormhole volume? Susskind conjectured that the dual quantity is the circuit complexity of the CFT state, which continues to increase even after the system equilibriates.

But Susskind's conjecture raises its own issues --- we show that for the kinds of quantum states in the CFT, their quantum circuit complexity is exponentially hard to approximate, whereas in the dual AdS space, the wormhole volume can be efficiently approximated. Or to put it in other words, the circuit complexity of the CFT states is not “feelable”, that is, it is not a quantity which can be observed with polynomial-time quantum experiments, in contrast to wormhole volume. One consequence is that the dictionary map which exhibits the AdS/CFT correspondence must itself be exponentially hard to compute. Formally, a key part of this argument appeals to a fundamental notion from cryptography known as computational pseudorandomness, where ensembles of states of low circuit complexity can masquerade as high complexity states to any casual observer.

The talk will be self contained and will include an introduction to the basic notions of computational pseudorandomness.

Based on joint work with Adam Bouland and Bill Fefferman.

**Organizers: Sanjeev Arora, Curtis Callan, and Victor Mikhaylov **“Deep learning” refers to use of neural networks to solve learning problems, including “learning” hidden structures in large and complex data sets. The theory for this field is still in its infancy. Lately physical and biological scientists have begun to explore how it might apply to their domains. This seminar series seeks to introduce the theoretical science community in Princeton and surrounding regions to the practice, promise, and problems of deep learning. It will consist of monthly afternoon sessions ---geared to the broader scientific community--- that will feature an invited talk followed by informal discussions among participants. The schedule will be updated whenever dates for new speakers are confirmed.This seminar series is coordinated with the “Special Year on Optimization, Statistics, and Theoretical Machine Learning” at the Institute for Advanced Study (under the direction of co-organizer Sanjeev Arora).**Register here: **http://pcts.princeton.edu/programs/current/deep-learning-for-physics-seminar-series/121

We will introduce ourselves and give a 2 minute description of what we are interested in at the moment.

The plan for future group meetings is to have some review talks, or topics for discussions. So please think about suggestions for things you would like to see discussed at future meetings. You can also think whether you want to volunteer for leading one of the discussions.

Conformal Field Theory (CFT) is a framework used to describe physical systems with no intrinsic length or energy scales. CFTs have wide applicability across theoretical physics, ranging from critical points in the phase diagrams of water or magnetic materials to the low-energy dynamics of extended objects in string theory. In this talk, I will begin by describing how CFTs can be used to understand critical phenomena. I will then discuss recent ideas that led to tremendous progress in obtaining a quantitative understanding of various corners in the space of all possible CFTs. I will end by discussing how CFTs can be used to describe and learn about Quantum Gravity in the presence of a negative cosmological constant.

We present a first-principles derivation of a weak-strong duality between the four-dimensional fishnet theory in the planar limit and a discretized string-like model living in AdS5. At strong coupling, the dual description becomes classical and we demonstrate explicitly the classical integrability of the model. We test our results by reproducing the strong coupling limit of the 4-point correlator computed before non-perturbatively from the conformal partial wave expansion. Next, by applying the canonical quantization procedure with constraints, we show that the model describes a quantum integrable chain of particles propagating in AdS5. Finally, we reveal a discrete reparametrization symmetry of the model and reproduce the spectrum when known analytically. Due to the simplicity of our model, it could provide an ideal playground for holography. Furthermore, since the fishnet model and N=4 SYM theory are continuously linked our consideration could shed light on the derivation of AdS/CFT for the latter. This talk is based on recent work with Nikolay Gromov.

In the next decade, improvements in the CMB and Large Scale Structure (LSS) measurements will make the universe an excellent laboratory for neutrino physics. Besides knowing the sum of neutrino masses, we can better answer questions about neutrino properties, such as how long the SM neutrinos can live? In this talk, I will explain the LSS signals of neutrino decay and show that the next generation LSS and CMB lensing measurements can either extend the lifetime bound on SM neutrinos to a cosmological time scale, or probe the distinct signatures of neutrino decay.

This talk will give a brief overview focused on six papers written by D. Gaiotto, G. Moore, and A. Neitzke

loosely centered around the topics mentioned in the title. The papers are on the arXiv.

Background reading: Some short reviews are:

https://arxiv.org/pdf/1211.2331.pdf

https://arxiv.org/pdf/1308.2198.pdf

https://arxiv.org/pdf/1412.7120.pdf

Some pedagogical/summer school lecture notes can be found in talks # 31, 35, 47, 84 on the home page of G. Moore:

http://www.physics.rutgers.edu/~gmoore/

Multiparticle production is studied experimentally and theoretically in QCD that describes interactions in the language of quarks and gluons. In the experiment the real hadrons are registered. For transfer from quarks and gluons to observed hadrons various phenomenological models are used.In order to describe the high multiplicity region, we offer a gluon dominance model (GDM). It represents a convolution of two stages. First stage is described as a part of QCD. For second one (hadronisation), the phenomenological model is used. To describe hadronisation, a scheme has been proposed, consistent with experimental data in the region of its dominance. Comparison of this model with data on $*e^*+*e^*-$ annihilation over a wide energy interval (up to 200 GeV) confirms the fragmentation mechanism of hadronisation, the development of the quark-gluon cascade with energy increase with a domination of bremsstrahlung gluons.The description of topological cross sections in $*pp$ *collisions within of GDM testifies that in hadron collisions the mechanism of hadronisation is being replaced by the recombination one. At that point, gluons play an active role in the multiparticle production process, and valence quarks are passive. They stay in the leading particles, and only the gluon splitting is responsible for the region of high multiplicity.GDM with inclusion of intermediate quark charged topologies describes topological cross sections in a proton-antiptoton annihilation and explains linear growth of a secondary correlative momentum in the negative area.The scaled variance of a neutral pion number mesuared by us is rising abruptly in the region of high total multiplicity and differs from Monte Carlo predictions by seven standard deviations. The growth of fluctuations of the neutral pion number in this region may indicate the formation of a pion (Bose-Einstein) condensate. Despite the growth of fluctuations on the neutral number, their average remains equal to 1/3 of the total pion number.

Quantising a black hole can be done starting with conventional physics. We just assume matter to keep the form of point particles until they come close to the horizon. The gravitational back reaction of these particles generates a novel relation between particles going in and particles going out, enabling us to transform in-going particles into out-going ones. This transformation removes “firewalls” along the future and past horizons, but it strongly affects space-time inside a black hole. It subsequently allows us, and indeed forces us, to identify antipodal points on the horizon. We argue that this exotic modification of the boundary condition is the only way to restore unitarity for the quantum evolution operator, and to identify the black hole microstates. Some mysteries, however, remain unresolved.

In this talk, based on work with S. Gubser, Z. Ji, B. Trundy, and A. Yarom, I present a scalar theory described by an action given in terms of a bi-local integral of a power law factor, with an exponent parameter s, multiplied by the squared arc length between points on the target manifold. Depending on the choice of s and of dimension, the theory can reduce to the usual sigma model, higher derivative versions thereof, or to a non-local theory with potential applications to the dynamics of M2-branes. I will also discuss the renormalization of the theory at one-loop level.

The dynamics and spread of quantum information in complex many-body systems is presently attracting

a lot of attention across various fields, ranging from cold atom physics via condensed quantum matter

to high energy physics and quantum gravity. This includes questions of how a quantum system thermalizes

and phenomena like many-body interference and localization, more generally non-classicality in many-particle

quantum physics. Here concepts that are based on echoes, i.e. rewinding time, provide a useful way to monitor complex quantum dynamics and its stability. Central to these developments are so-called out-of-time-order correlators (OTOCs) as sensitive probes for chaos and the temporal growth of complexity in interacting systems.

We will address such phenomena for quantum critical and quantum chaotic systems using semiclassical path

integral techniques based on interfering Feynman paths, thereby bridging the classical and quantum many-body world and allowing for deriving random matrix results. These methods enable us to compute echoes and

OTOCs including entanglement and correlation effects. Moreover, on the numerical side we devise a

semiclassical method for Bose-Hubbard systems far-out-of equilibrium that allows us to calculate many-body

quantum interference on time scales far beyond the famous Ehrenfest/scrambling time.

I will discuss walking behavior in gauge theories and weakly first order phase transition in statistical models. Despite being phenomena appearing in very different physical systems, they both show a region of approximate scale invariance. They can be understood as a RG flow passing between two fixed points living at complex couplings, which we call complex CFTs. By using conformal perturbation theory, knowing the conformal data of the complex CFTs allows us to make predictions on the observables of the walking theory. I will also discuss some two-dimensional examples.

Recent work has introduced a correspondence between jets and natural languages. In this talk, I will review how machine learning, with this natural language processing point of view, is changing the way we are thinking about jets. First, I will describe a very effective model for classification and regression tasks. Next, I will introduce a simplified model to aid in machine learning research for jet physics, that captures the essential ingredients of parton shower generators in full physics simulations. I will discuss how this line of research provides new insights into jets substructure and could lead to a systematic fit of a physics model to data.

This is a satellite event in association with the annual `Origins of the Universe' conference that takes place Sept 26-27, 2019 at the Simons Foundation in New York City's Flatiron District.

Confirmed Speakers:

- Bruce Allen (Max Planck Institute for Gravitational Physics)
- Beverly Berger (Stanford University)
- Thibault Damour (IHES)
- Karsten Danzmann (Max Planck Institute for Gravitational Physics)
- Sean McWilliams (West Virginia University)
- Slava Mukhanov (Ludwig-Maximilians-University, Munich)
- Igor Rodnianski (Princeton University)
- Richard Woodard (University of Florida, Gainesville)

I will discuss recent progress about the Cardy-like asymptotics of 4d supersymmetric index on S^3, also known as superconformal index. The main observation is that Bose-Fermi cancellation that trivializes the asymptotic expression of the index can be obstructed by complexifying chemical potentials. Applied to N=4 SYM, the new asymptotic free energy reproduces the Bekenstein-Hawking entropy of the known 1/16 BPS black hole in AdS5. If time permits, I will also talk about some circumstantial evidences for new BPS black holes. (References: 1810.12067, 1811.08646, 1904.03455.)

Using our state-of-the-art code Fornax we have simulated the collapse and explosion of the cores of many massive-star models in three spatial dimensions. This is the most comprehensive set of realistic 3D core-collapse supernova simulations yet performed and has provided very important insights into the mechanism and character of this 50-year-old astrophysical puzzle. I will present detailed results from this suite of runs and the novel conclusions derived from our new capacity to simulate many 3D, as opposed to 2D and 1D, full physics models every year. This new capability, enabled by this new algorithm and modern HPC assets, is poised to transform our understanding of this central astrophysical puzzle.

We review a recent geometric formulation of the tree-level S-matrix of various quantum field theories, including gauge and gravity theories, in terms of intersection numbers of twisted cohomology groups on the moduli space of genus-zero curves with marked points. Scattering amplitudes are computed in terms of integrals over such moduli spaces that localize on worldsheets resembling Feynman diagrams and in certain circumstances coincide with the field-theory limit of string theory. We outline recursion relations that allow for explicit computations of S-matrices on the forgetful fibration of moduli spaces. We show that in the massless limit intersection numbers have another localization formula on the critical points of a certain Morse function.

We construct a general form for an F-theory Weierstrass model over any base giving a 6D or 4D supergravity theory with gauge group SU(3) x SU(2) x U(1) / Z_6 and associated generic matter. The concept of 'generic matter' can be rigorously defined in 6D supergravity and generalizes naturally to four dimensions for F-theory models. We describe general F-theory models with this gauge group and the associated generic matter content, which fit into two distinct classes, and present an explicit Weierstrass model that realizes these models as two distinct branches. We also discuss, as a special case, the class of models recently studied by Cvetic, Halverson, Lin, Liu, and Tian, for which we demonstrate explicitly the possibility of unification through an SU(5) unHiggsing.

My talk is devoted to studies of large N saddle point structures in the SYK model beyond the commonly used approximations, in particular the replica-diagonal assumption and the conformal limit. We will discuss new solutions of the saddle point equations in the SYK and their role in physics of the model and in the gravity dual description. We will focus on the replica-nondiagonal exact saddle points, which introduce small nonperturbative effects in the 1/N expansion of SYK. We will consider their properties and implications for the gravity dual, a UV completion of JT gravity.

The talk is based on papers arXiv:1811.04831, arXiv:1905.04203 and on current work in progress.

Axion and Axion-like particles are fascinating dark matter candidates and a great effort has been devoted to their study, both theoretically and experimentally. In this talk I will discuss two different astrophysical searches. The first one consists in looking with radio telescopes for the spontaneous decay of axion dark matter using different targets as Dwarf Galaxies, Clusters or the Galactic Center. The second one uses the parity violating axion interactions to exploit the extreme precision of pulsar timing measurements and look for oscillations in the polarization angle of the pulsar signal.

Gauge/gravity duality relates certain strongly coupled CFTs with large effective central charge to semi-classical gravitational theories with AdS asymptotics. I will describe recent progress in understanding gravity duals for CFTs on non-trivial spacetimes with black hole horizons. Such gravity methods provide powerful new tools to access the physics of these strongly coupled theories, which often differs qualitatively from that found at weak coupling. I will then use some of the intuition gather from these studies to motivate the existence of static black holes in Randall-Sundrum II braneworlds. If time permits, I will discuss some of its properties such as dynamical stability.Reading material: arXiv:1104.4489, arXiv:1105.2558, arXiv:1208.6291, arXiv:1212.4820, arXiv:1405.2078, arXiv:1604.04832

Moiré patterns are ubiquitous in layered van der Waals materials and can now be fabricated with considerable control by combining mechanical exfoliation of van der Waals layers with tear and stack device fabrication techniques. I will explain why the electronic and optical properties of two-dimensional semiconductors and semimetals are strongly altered in long-period moiré superlattices, focusing in particular on the remarkable example of twisted bilayer graphene. When twisted to a magic [1] relative orientation angle near 1 degree the moiré superlattice minibands of bilayer graphene become extremely narrow and electronic correlations become strong. Experimental studies [2] of magic-angle twisted bilayer graphene (MATBG) have demonstrated that the electronic ground state can be a superconductor, a metal, or an insulator, depending on the filling of the magic angle flat bands. Insulating states occur close to most integer values of the number of electrons per moiré superlattice period, whereas superconducting states are common at fractional moiré band filling factors. In some cases, the insulating states are purely orbital ferromagnets that exhibit a quantum anomalous Hall effect and have superlattice bands with non-zero topological Chern indices C. I will discuss progress that has been made toward understanding these remarkable properties.[1] Moire bands in twisted double-layer graphene, R. Bistritzer and A.H. MacDonald, PNAS 108, 12233 (2011). [2] Magic-angle graphene superlattices: a new platform for unconventional superconductivity, Y. Cao et al. Nature (2018).

This talk will review the structure of closed superstring scattering amplitudes with particular emphasis on the constraints imposed by various dualities. This leads to precise determination of the coefficients of low order terms in the low energy expansion of amplitudes in theories with maximal supersymmetry. Among other things, these results provide "data" that should be matched by the holographic connections with conformal field theories.

It is widely believed that long after gravitational collapse, the external geometry of black holes relaxes to the Kerr-Newman solution. In contrast, the interior geometry is not unique and depends on initial conditions. I will discuss universal features of the interior of one-sided black holes in asymptotically flat space with a scalar field. In particular, I will argue that generically there exists effective gravitational shocks at the would-be inner horizon, a singular Cauchy horizon, and a spacelike singularity at r = 0.

Lifshitz scaling is an anisotropic scaling where time and space scale differently. Quantum field theories that exhibit Lifshitz scale symmetry provide a framework for studying low energy systems with an emergent dynamic scaling such as quantum critical points. Introducing supersymmetry to the Lifshitz algebra leads to a rich structure that is less constrained compared to that of relativistic supersymmetry. We construct supersymmetric Lifshitz quantum field theories and study their renormalization properties and RG flows. We show that models of Lifshitz supersymmetry that possess a holomorphic structure realize lines of quantum exact Lifshitz fixed points for various choices of spacetime dimensions and marginal supersymmetric interactions. The presented results are based on two papers.

String theory on AdS3xS3xT4 with one unit of NSNS flux has been recently argued to be dual to the symmetric product orbifold of T^4. The duality has been extended to the case of generic NSNS background flux. I will consider the bosonic version of this duality and show how to match null-vector constraints on three-point functions. I will explain how some three-point functions can be explicitly derived and matched on the two sides of the duality. This amounts to one of the very first holographic matches of non-protected AdS3/CFT2 correlators.

Conventionally, the main focus for the cosmic evolution of our universe has been on descriptions in terms of particles: dark matter (DM) as massive particle, and dark radiation, if existing at all, in the form of massless or very light particle. In this talk, I will discuss a scenario where conformal field theory (CFT) plays a crucial role in cosmology, especially production of naturally light dark matter. When the Standard Model (SM) couples to a sector of CFT, I will argue that in the regime where only the SM sector gets reheated, the energy density of the CFT sector is populated via energy injection from the SM (conformal freeze-in) and can be reliably computed. Such CFT energy density, redshifting like a radiation, will not account for DM unless somehow a mass gap is generated in the CFT. Remarkably, such a gap scale is dynamically generated due to phase transitions of SM: electroweak and QCD. In this way, DM energy today is produced in the early universe when it is not in gapped particle state, but a CFT state. Moreover, DM mass scale consistent with observed relic density and other observational constraints (mostly bullet cluster and warm dark matter bounds) turns out to be less than MeV. Therefore, conformal freeze-in provides a framework for naturally light DM.

The EHT Collaboration has recently published images of the supermassive black hole in M87. The images are dominated by a bright ring-like structure with an angular brightness asymmetry. While the diameter of this ring is resolved by the EHT, its thickness and detailed substructure are not. General relativity predicts that within this image lies a thin “photon ring,” composed of an infinite sequence of bright self-similar subrings. I will discuss the theoretical aspects of these general features of astrophysical black hole images, as well as the potential observability of the photon ring at extensions of the EHT.

Reading material:

arXiv:1907.04329, arXiv:1906.11242, arXiv:1905.11406

In this talk, I will discuss the idea that the exact one-loop free energy of the static patch of D-dimensional de Sitter space can be computed as a simple integral transform of an SO(1;D) bulk character corrected by an SO(1; D-2) edge character, for fields of arbitrary mass and spin. The bulk character captures the particle content of the theory and counts quasinormal modes in the bulk. The edge character counts edge modes on the horizon. I will also show the application of this formalism in 4D and 3D dS Vasiliev gravity. In the 4D case, after summing over spins, there is a huge cancellation between the bulk and edge characters, leaving the character of a scalar living in three dimensions. In the 3D case, I will discuss its relation with Chern Simons theory.

It is currently not well understood whether the holographic principle can be applied to asymptotically flat space-times. This talk will consider a flat limit of AdS/CFT that leads to a formula relating S-matrix amplitudes in flat space and conformal correlators in AdS/CFT. I will explain how to use the formula to compute S-matrices in simple examples, and I will discuss how to recast flat space physics concepts in the language of conformal field theory and holography. I will also discuss IR divergences and the construction of an IR finite S-matrix using AdS/CFT.

When absorbing boundary conditions are used to evaporate a black hole in AdS/CFT, we show that there is a phase transition in the location of the quantum Ryu-Takayanagi surface, at precisely the Page time. The new RT surface lies slightly inside the event horizon, at an infalling time approximately one scrambling time in the past. We can immediately derive the Page curve, using the Ryu-Takayanagi formula, and the Hayden-Preskill decoding criterion, using entanglement wedge reconstruction. Becausepart of the interior is now encoded in the early Hawking radiation, the decreasing entanglement entropy of the black hole is exactly consistent with the semiclassical bulk entanglement of the late-time Hawking modes, despite the absence of a firewall. By studying the entanglement wedge of highly mixed states, we can understand the state dependence of the interior reconstructions. Directly after the Page time, interior operators can only be reconstructed from the Hawking radiation if the initial state of the black hole is known. As the black hole continues to evaporate, reconstructions become possible that simultaneously work for a large class of initial states. This state dependence provides the mechanism by which information that falls into the black hole eventually escapes in the Hawking radiation.

We perform high resolution simulations in a scenario where the Peccei-Quinn (PQ) symmetry is broken after inflation starting at the epoch before the PQ phase transition and ending at matter-radiation equality. We characterize the spectrum of primordial perturbations that are generated and comment on implications for efforts to detect axion dark matter (DM). We also measure the DM density at different simulated masses and argue that the correct DM density is obtained for an axion mass of 25.2 ± 11.0 µeV.

I will review some old ideas about the duality between matrix models and Liouville theory coupled to a (p,q) minimal model. In this approach t'Hooft diagrams of the matrix model are thought of as a discretization of a 2d surface. Fine-tuning of the coupling constant leads to divergence of the perturbative expansion. In this limit dense t'Hooft diagrams dominate and become a good approximation of a smooth 2d surface.

Reading material:

hep-th/9306153; hep-th/9304011; Seiberg, "Notes on quantum Liouville theory and quantum gravity"; Lecture notes by Zamolodchikov brothers http://qft.itp.ac.ru/ZZ.pdf

The asymptotic symmetry algebra of asymptotically flat spacetimes implies an infinity of conserved charges for 4D scattering which can be neatly recast as 2D conformal Ward identities. We cover recent progress on the proposed 4D/2D dictionary starting from the conformally soft modes that appear as currents and extending our map to a basis for finite energy scattering states.

We study the effect of ZZ instantons in c = 1 string theory, and demonstrate that they give rise to non-perturbative corrections to closed string scattering amplitudes that do not saturate unitarity within the closed string sector. Beyond the leading non-perturbative order, logarithmic divergences are canceled between worldsheet diagrams of different topologies, due to the Fischler-Susskind-Polchinski mechanism. These results also allow us to propose the exact non-perturbative matrix model dual of c=1 string theory.

**Registration for each event is free, but required. Please click on the registration link below for each date, as it becomes available.**Talk #1: Machine Learning Techniques for Many-Body Quantum SystemsIn this introductory seminar I will cover the main machine learning techniques so-far adopted to study interacting quantum systems. I will first introduce the concept of neural-network quantum states [1], a representation of the many-body wave-function based on artificial neural networks. Theoretical aspects of these representations, including the problem of including symmetries, and their entanglement capacity will be discussed. Then, I will show how neural-network quantum states can be used in a variety of applications. Examples will be given for data-driven, experimental analysis in the context of quantum state tomography [2]. I will also show how these states can be used in variational applications to theoretically study the physical properties of interacting many-body matter, highlighting recent applications to frustrated magnetism [3] and fermionic systems [4].[1] Carleo, and Troyer - Science 355, 602 (2017); [2] Torlai, et al. - Nature Physics 14, 447 (2018); [3] Choo, et al. - arXiv:1903.06713 (2019); [4] Pfau, et al. - arXiv:1909.02487 (2019).Talk #2: Autoregressive Simulation of Many-body Quantum SystemsUnderstanding phenomena in systems of many interacting quantum particles, known as quantum many-body systems, is one of the most sought-after objectives in contemporary physics research. The challenge of simulating such systems lies in the extensive resources required for exactly modeling quantum wave-functions, which grows exponentially with the number of particles. Recently, neural networks were demonstrated to be a promising approximation method of quantum wave functions. However, thus far, this approach was mostly focused on more traditional architectures such as Restricted Boltzmann Machines and small fully-connected networks. In this talk, we propose a method for scaling this approach to support large modern architecture. Though significantly more expressive, such architectures do not lend themselves to the conventional methods for employing neural networks for simulating quantum systems. A key part of the simulation is to sample according to the underlying distribution of particle configurations. Current methods rely on Markov-Chain Monte-Carlo sampling, which is too expensive for use with modern architectures, effectively limiting their usable size and capacity. Inspired by recent generative models, we propose a specialized deep convolutional architecture that supports efficient and exact sampling, completely circumventing the need for Markov Chain sampling. We demonstrate our approach can obtain accurate results on larger system sizes than those currently accessible to other neural-network representation of quantum states.

Functional methods, in particular efficient reorganization of the one-loop effective action, have recently made a reappearance in simplifying the problem of computing matching and running effects in Lorentz-invariant effective field theories (EFTs) such as the Standard Model Effective Field Theory. This has lead to the appearance of universal one-loop effective actions, where such effects are now known in closed form for arbitrary field-content. These insights have not yet been brought to bear on modern kinematic EFTs such as heavy quark (HQET) and soft-collinear effective theory despite their greater focus on precision and the inclusion of higher-order effects. I will present some first steps in developing functional one-step matching formulae for EFTs where Lorentz symmetry is broken (or at least obscured) using HQET as my focus but also commenting on more complicated multi-mode EFTs as well.

We review some infinite dimensional symmetries that appear in dimensionally reduced classical general relativity. Reducing from d=4 to d=2 gives a two dimensional nonlinear sigma model with an infinite dimensional affine Kac-Moody symmetry called the Geroch group. Further reducing to d=1 (along a null Kill vector) enhances the Geroch group to a mysterious "hyperbolic Kac-Moody" symmetry.Further reading:

[1] P. Breitenlohner and D. Maison, "On the Geroch group," Ann. Inst. H. Poincare, 46, 215 (1987)

[2] H. Nicolai, "Two-dimensional gravities and supergravities as integrable systems," in “Schladming 1991, Proceedings, Recent aspects of quantum fields,” 231, and Hamburg DESY 91-038

[3] H. Lu, M. Perry, and C. Pope, ArXiv:0711.0400 and ArXiv:0712.0615

Recently, an exact AdS3/CFT2 duality was proposed. String theory on AdS3xS3xT4 with one unit of pure NS-NS background flux was conjectured to be dual to the symmetric product orbifold of T4. This is established at the level of the full spectrum of the CFT. In this talk I will report on the matching of sphere correlation functions. This involves crucially the so-called spectrally flowed representations. The moduli space integral of n-point functions for n>3 is argued to localise to a finite sum. I will also discuss the corresponding classical solution of the SL(2,R) WZW model and show that their on-shell action precisely reproduce the correlation functions in the symmetric product orbifold as calculated by path integral methods.

I will discuss time-dependent probes of the renormalization group, and derive new constraints that govern the spread of local operators in holographic theories. The same methods lead to sum rules for inflationary correlators, relating observables, like the speed of sound during inflation, to properties of the UV theory.

We consider supersymmetric twist and omega deformation of a type IIB brane setup involving N D3 and K D5 branes. In the large N limit, this leads to a holographic duality between two topological/holomorphic theories. We compute certain operator algebras from both sides of this topological holographic duality and find the result consistent with the claimed duality. The algebra we compute is the Yangian of gl_K, which is the symmetry algebra of an integrable spin chain. In addition, the instance of topological holography that we find is an example supporting Costello's proposal relating holography and Koszul duality.

We analyze modular invariance drawing inspiration from tauberian

theorems. Given a modular invariant partition function with a positive

spectral density, we derive lower and upper bounds on the number of

operators within a given energy interval. They are most revealing at high

energies. In this limit we rigorously derive the Cardy formula for the

microcanonical entropy together with optimal error estimates for various

widths of the averaging energy shell. Finally, we identify a new universal

contribution to the microcanonical entropy controlled by the central

charge and the width of the shell.

NOTE: LUNCH WILL BE HELD AT 12:00 PM IN THE SPACE NEXT TO THE PCTS SEMINAR ROOM.I will describe our continuing work for extracting the most of the LIGO-VIRGO data. In this talk, I will discuss the process that was used to characterize the impact of non-Gaussian phenomena (so called 'Glitches') I will then discuss the process that exploited the found properties in order to rank candidates based on one detector alone. I will then discuss how these candidates are then verified using very little information in the less sensitive detector. Using this, we found two new events. One (GW170817A) is the highest mass event reported to date. The other (GWC170402) was also very interesting, as there are some solid signs for the expression of higher modes, but a full coherent GR solution that explains the signal is still lacking. Last, I will discuss the implications of this method for the future analysis of the ongoing third observing run of the LIGO-VIRGO data.

The SYK Model was originally introduced as a random matrix model for the nuclear interaction that also describes the exponential rise of the spectral density known as the Bethe formula. Exactly this behavior is the hallmark of the Schwarzian action, the low energy limit of the SYK model, which is the main reason for the excitement this model has brought to the field of Quantum Gravity. Another phenomenon in chaotic many-body quantum systems is the existence of collective excitations. Remarkably, they are present in the Maldacena-Qi model of two SYK models coupled by a spin-spin interaction, which describes a phase transition between two black holes and a thermal phase. The collective state is the ground state which is close to a Thermo-Field Double state. We find that for systems that can be studied numerically, the wave functions of the ground state show substantial deviations from the Thermo-Field Double state, which suggests a non-uniform convergence to this state in the limit of a large number of particles. The main topic of this talk is the discussion of the thermodynamical and spectral properties of the Maldacena-Qi Model. We find a transition from Poisson statistics in the tail of the the spectrum to RMT statistics at higher energies, when we separate the Hamiltonian according to the spin mod 4 symmetry. We relate this order-chaos transition to the Hawking-Page phase transition.

The Born-Infeld model is an effective field theory of central importance describing the low-energy dynamics of massless gauge bosons on the world-volume of D-branes. Though it is in many ways an exceptional model of nonlinear electrodynamics, several aspects of the physics of the Born-Infeld model remain mysterious. In this talk I will explain how aspects of the model, obscured in the traditional formulation of Lagrangian field theory, are clarified by directly studying the on-shell S-matrix. In particular in 3+1-dimensions, classical Born-Infeld has an electromagnetic duality symmetry which manifests in tree-level scattering amplitudes as the conservation of a chiral charge. Whether this conservation law can be preserved under perturbative quantization is presently unknown. Using modern scattering amplitudes techniques, we have initiated a study of the S-matrix of Born-Infeld at one-loop. I will describe how generalized unitarity together with supersymmetric decomposition can be used to explicitly calculate infinite classes of one-loop amplitudes, and explain how the results are consistent with the existence of a quantum electromagnetic duality.

This talk will follow the discussions found in https://arxiv.org/abs/1711.04773 and https://arxiv.org/abs/1902.04082. We will discuss the cosmological implications of the Co-Decaying Dark Matter Model--a recently proposed mechanism for depleting the density of dark matter through the decay of nearly degenerate particles. This model generically predicts the existence of an Early Matter Dominated phase of universe evolution. We will show that this phase promotes sub-structure growth and solar mass primordial black holes.

The physics of systems with quenched random disorder reveals behavior qualitatively different from that found in systems with translational symmetry, continuous or discrete. The seminal work by Anderson over six decades back [1] established the phenomenon of electron localization in a model of non-interacting electrons and showed the existence of a metal-insulator (extended-localized) transition in three dimensions. Since then, a host of interesting phenomena have been uncovered, exploring e.g., the role of system dimensionality, the impact of breaking time-reversal and other symmetries, the influence of electron-electron interactions, and the effects of rare fluctuations.In this talk I will describe some of these through illustrative examples we have explored in the past several decades, using platforms where semiconductors act as the vacuum. I will discuss in particular (i) magnetic behavior of doped semiconductors below and above the insulator-metal transition [2-4], (ii) magnetism in diluted magnetic semiconductors at low electron density [5,6], and, if time permits, (iii) many-body electron localization in two dimensions in the quantum Hall regime [7.8].[1] P. W. Anderson, Physical Review **109**, 1492 (1958).

[2] R. N. Bhatt and P. A. Lee, Physical Review Letters** 48**, 344 (1982).

[3] M. Milovanovic, S. Sachdev and R. N. Bhatt, Physical Review Letters **63**, 82 (1989).

[4] R. N. Bhatt and D. S. Fisher, Physical Review Letters **68**, 3072 (1992).

[5] Xin Wan and R. N. Bhatt, International Journal of Modern Physics C **10**, 1459 (2000).

[6] Mona Berciu and R. N. Bhatt, Physical Review Letters **87**, 107203 (2001).

[7] Scott D. Geraedts and R. N. Bhatt, Physical Review B **95**, 054303 (2017).

[8] Akshay Krishna, Matteo Ippoliti and R. N. Bhatt, Physical Review B **89**, 041111(R) (2019); Physical Review B **100**, 054202 (2019).

Attendance is free, but space is limited, so please register! **Speakers:**

- Sheperd Doeleman
- Robbert Dijkgraaf
- Wendy Freedman
- Gabriela Gonzalez
- Theodore Jacobson
- Sergiu Klainerman
- Nergis Mavalvala
- Robert Myers
- Malcolm Perry
- Andrew Strominger
- Neil Turok
- William Unruh

The Event Horizon Telescope (EHT) is a Very Long Baseline Interferometry (VLBI) array operating at the shortest possible wavelengths, which can resolve the event horizons of the nearest supermassive black holes. Observing at mm radio wavelengths enables detection of photons that originate from deep within the gravitational potential well of the black hole, and travel unimpeded to telescopes on the Earth. The primary goal of the EHT is to resolve and image the predicted ring of emission formed by the photon orbit of a black hole and to eventually track dynamics of matter as it orbits close to the event horizon. A sustained program of improvements to VLBI instrumentation and the addition of new sites through an international collaborative effort led to Global observations in April 2017: the first campaign with the potential for horizon imaging. After 1.5 years of data reduction and analysis we report success: we have imaged a black hole. The resulting image is an irregular but clear bright ring, whose size and shape agree closely with the expected lensed photon orbit of a 6.5 billion solar mass black hole. This talk will cover the project and first results as well as future directions for a next-generation instrument that is aimed at real-time black hole video.

We are living in the golden era of gravitational research, realizing Einstein’s vision that by studying the geometry of space and time we can determine the origin, composition, and fate of the Universe. Cutting-edge technology has opened up many new windows in science, from the detection of the remnants of the Big Bang and gravitational waves to the image of a supermassive black hole. Yet, deep questions remain about the dark matter, dark energy, and the nature of quantum space-time.

**Speakers:**

- Sheperd Doeleman
- Robbert Dijkgraaf
- Wendy Freedman
- Gabriela Gonzalez
- Theodore Jacobson
- Sergiu Klainerman
- Nergis Mavalvala
- Robert Myers
- Malcolm Perry
- Andrew Strominger
- Neil Turok
- William Unruh

I will present my recent results on the behavior of solutions to the Klein-Gordon equation on the interior of Reissner-Nordstöm-AdS and Kerr-AdS. Despite the very slow logarithmic decay in the exterior, I show that linear waves arising from smooth data with Dirichlet boundary conditions at infinity remain bounded on the Cauchy horizon for Reissner-Nordström-AdS. For Kerr-AdS, however, the situation is far more delicate: Depending on the Diophantine properties of the ratio of the black hole parameters, linear waves blow up or remain bounded at the Cauchy horizon of Kerr-AdS.

I will explain how the S-matrix Bootstrap for massless particles can be used to constrain the space of Effective Field Theories (EFT). In particular, I will discuss the S-matrix bootstrap for massless particles in unitary, relativistic two dimensional quantum field theories. In the context of flux tube physics, this allows us to constrain several terms in the S-matrix low energy expansion or -- equivalently -- on Wilson coefficients of several irrelevant operators showing up in the flux tube effective action. The S-matrices living at the boundary of the allowed space exhibit an intricate pattern of resonances with one sharper resonance whose quantum numbers, mass and width are precisely those of the world-sheet axion previously proposed. Finally, I will present work in progress on pion scattering amplitudes and the chiral Lagrangian. The general method should be extendable to other massless S-matrices including gauge and gravity theories.

One generic scenario for the dark matter of our universe is that it resides in a hidden sector: it talks to other dark fields more strongly than it talks to the Standard Model. I'll discuss some minimal cosmological origin scenarios for this class of models and explore their consequences for the observability of dark states today. Some results of interest include simple, WIMP-y models of dark matter with parametrically novel behavior.

Phosphorus atoms qubits in silicon have demonstrated extremely long (up to 35 s) coherence times with >99.9% fidelity in the highly manufacturable material silicon. Their small size, combined with the magnetically quiet environment of isotopically pure silicon, make them analogous to ion trap qubits but in a scalable solid-state system. One of the long-term challenges for semiconductor qubits is to understand, and control, the local electromagnetic environment of the qubit down to sub 10nm length scales. Scanning probe techniques, combined with molecular beam epitaxy allow us to engineer fully crystalline devices at the atomic scale and directly probe the qubit wave function with exquisite precision. We will discuss the progress and vision for this approach.

We describe the coupling of holomorphic Chern-Simons theory at large N with Kodaira-Spencer gravity. This gives a complete description of open-closed string field theory in the topological B-model. We explain an anomaly cancellation mechanism at all loops in perturbation theory in this model. At one loop this anomaly cancellation is analogous to the Green-Schwarz mechanism. This is joint work with Kevin Costello.

Because of the Black-Hole Information Paradox, and the singularity, many physicists believed that GR must be modified to incorporate quantum effects, and that such modifications may affect black-hole spacetimes. The additional near-horizon structure might modify the boundary conditions for incoming gravitational waves, and lead to gravitational wave echoes. These echoes will then become the "smoking gun" of modifications to relativity. Therefore parametrizing gravitational echoes and searching for them will be an important way to quantify how "black" the black holes really are. In this talk, I will talk about the theoretic formulation of gravitational wave echoes, and point out the current issues associated with this idea.

I will describe my work, all joint with D. Gaiotto and some also joint with E. Witten, to understand the homotopy type of the space of (1+1)d N=(0,1) SQFTs --- what a condensed matter theorist would call "phases" of SQFTs. Our motivating hypothesis (due in large part to Stolz and Teichner) is that this space models the spectrum called "topological modular forms". Our work includes many nontrivial checks of this hypothesis. First, the hypothesis implies constraints on the possible values of elliptic genera, and suggests (but does not imply) the existence of holomorphic SCFTs saturating these constraints; we have succeeded in constructing such SCFTs in low central charge. Second, the hypothesis implies the existence of torsion-valued "secondary invariants" beyond the elliptic genus that protect SQFTs from admitting deformations that spontaneously break supersymmetry. I will explain such an invariant in terms of holomorphic anomalies and mock modularity.

**Registration for each event is free, but required. Please click on the registration link below for each date, as it becomes available. ****Register here: **

https://docs.google.com/forms/d/e/1FAIpQLScD1ZGB17mwhZ3cvyvs8vEqArGJknmcn_udUgL4tJm4DatmUA/viewform Abstract Talk #1: The initial breakthroughs of deep learning came in the form of predictive tasks such as image classification, where discriminative models were trained with supervised learning algorithms. More recently, there have been exciting developments for generative models trained with unsupervised learning algorithms. Generative models approximate the distribution of the data and open up a wider range of possible applications. Generative Adversarial Networks (GANs) are the most well known of these models; however, they have drawbacks. I will describe an alternative approach called normalizing flows and discuss them in the context of three physics problems: effective field theory measurements at the LHC, lattice quantum chromodynamics, and modeling the density matrix of a quantum system.Abstract Talk #2: String theory is a theory of quantum gravity that has had strong impacts on theoretical physics and mathematics. In this talk I will describe ways in which deep learning may lead to progress in string theory, with a special focus on broad applications in the string theory landscape. Known properties of the landscape and its relation to computational complexity will be briefly discussed, including ways in which the structure of the theory allows for the avoidance of worst-case complexity; for instance, networks of extra-dimensional spaces connected by topology changing transitions can aid in solving physically relevant Diophantine problems. The talk will focus on two types of problems in string theory. First, generative models will be discussed as a means for approximating statistical predictions, which are crucial given the large landscape of solutions. As a simple application, a conditional Wasserstein DCGAN will be used to learn random matrix approximations to Kahler metrics on Kahler moduli space, which are relevant for the physics of axion-like particles. Second, we will discuss multi-task search problems that arise in the landscape. A reinforcement learning A3C agent will be utilized to solve a multi-task problem in type IIA compactifications on a toroidal orbifold. Significant improvement over a random walker is achieved, a known human strategy is learned by the agent, but an RL-discovered strategy performs about twice as well.

Motivated by theories of neutral naturalness, I will argue that Mirror Stars are a generic possibility in any hidden sector with analogues of Standard Model electromagnetism and nuclear physics. I will show that if there exists a tiny kinetic mixing between the dark and SM photon, Mirror Stars capture SM matter from the interstellar medium, which accumulates in the Mirror Star core. This leads to a spectacular and distinctive signature that could be discovered in optical and X-ray searches.

Suggested reading:

Marc Mars, Present Status of the Penrose Inequality, arXiv:0906.5566

Netta Engelhardt and Gary Horowitz, A Holographic Argument for the Penrose Inequality in AdS, arXiv:1903.00555

Quantum Penrose Inequality, arXiv:1908.02755

The Wilsonian paradigm suggests universality of quantum field theory in the infrared. Interestingly, it also suggests universality of quantum mechanics (d=1 quantum field theory) in the *ultraviolet*. This suggests a study of the landscape of the infrared and the robustness of the ultraviolet. I will introduce and solve an infinite class of integrable deformations to quantum mechanics, focusing on a particular deformation inspired by the T-Tbar deformation of two-dimensional quantum field theory. In the context of holography, I will show how these deformations modify Jackiw-Teitelboim gravity in AdS_2. I will also present an equivalent description of the T-Tbar deformation in terms of coupling to worldline gravity. Applications to the Schwarzian theory and SYK will be discussed.

We are now experiencing a revolution in optical technologies, where one can print and control massive optical circuits, on a microelectronic chip. This revolution is enabling a whole range of applications that are in need for scalable optical technologies and it is opening the door to areas that only a decade ago were unimaginable.In the past decade, the photonic community witnessed a complete transformation of optics. We went from being able to miniaturize a handful of devices to being able to define and control the flow of light using thousands of monolithically integrated optical components – all on a silicon chip. The main drive for silicon photonics is the ability to transmit and manipulate ultra high bandwidth with low power dissipation. Today there are hundreds of products being developed and commercialized towards this goal.The field of silicon photonics is rapidly evolving and is now enabling completely new applications, ranging from Lidar to biomedical devices. This is partly due to the development of novel chip-scale technologies, novel devices and novel materials compatible with silicon photonics. Many of these technologies and devices can manipulate light across the whole VIS, IR and the Mid IR spectrum. I will discuss these emerging applications, as well as the advancement brought by these novel devices and materials.The key challenges of the field relate to the scalability of the systems in bandwidth, size and power. Some of these challenges are fundamental and require innovations that break traditional tradeoffs. Novel approaches for switching, modulating and amplifying light have emerged that can open the door to applications that rely on such scalable systems. I will describe the challenges of the field and some of the recent innovations that can potentially address these challenges.

The Kerr-Newman spacetime is the most general explicit black hole solution, and represents a stationary rotating charged black hole. Its stability to gravitational and electromagnetic perturbations has eluded a proof since the 80s in the black hole perturbation community. As put by Chandrasekhar, "the methods that have proved to be so successful in treating the gravitational perturbations of the Kerr spacetime do not seem to be applicable for treating the coupled electromagnetic-gravitational perturbations of the Kerr-Newman spacetime". He adds, "the principle obstacle is in finding separated equations".

Following the road map that mathematicians have taken in interpreting in physical space the known mode analysis, we will present a way to overcome "the apparent indissolubility of the coupling between the spin-1 and spin-2 fields in the perturbed spacetime". We will explain how the decomposition in modes, done to simplify the analysis of the equations, makes them unsolvable when electromagnetic and gravitational radiations interact. We instead generalize the Chandrasekhar transformation to Kerr-Newman in physical space and use it to obtain a quantitative proof of stability.

While the flat space two-body problem is integrable, the generally-relativistic one is not starting at the next-to-leading order.

In the appropriate classical limit, scattering amplitude-based techniques can yield the classical interaction of massive bodies to all orders in their velocities and to fixed order in the expansion in Newton's constant, that is a fixed order in the post-Minkowskian (relativistic weak-field) expansion.

In this talk we review an amplitudes-based framework for such calculations and the derivation of the third order in the post-Minkowskian expansion for the conservative Hamiltonian of a compact spinless binary system. We also describe the scattering angle at this order as well as a first comparison with numerical GR.

There is currently a (possible) tension between various measurements of the Hubble expansion rate. I will give a recap of this issue, and describe how we use the Cosmic Microwave Background to infer the local expansion rate. I will explain what assumptions we usually make about the cosmological model in doing so, and what kinds of early-universe modifications could bring some of the different measurements better in line. I will talk about new measurements we are making in Chile to improve estimates of the Hubble constant from the CMB, and to test alternative models.

With the detection of GW170817 we have observed the first multi-messenger gravitational wave signal from two merging neutron stars. This signal carried a multitude of information about the underlying equation of state (EOS) of nuclear matter, which so far is not known for densities above nuclear saturation. In particular it is not known if exotic states or even a phase transition to quark matter can occur at densities so extreme that they cannot be probed by any ground-based experiment. I will show how the information carried in the gravitational wave signal of GW170817 can be used to constrain the EOS at densities above saturation and what we can learn about the possible existence of phase transitions.I will also comment on how we can improve on those limits with upcoming observations of the NICER mission.

In the second part of the talk,I will focus on yet to be observed electromagnetic precursor emission from neutron star mergers. These precursors have the potential to provide complementary insights into the properties of neutron stars, such as their spins, which cannot yet be reliably extracted from the gravitational wave signal. I will present preliminary results on the interaction of force-free magnetospheres in compact binaries and demonstrate how powerful electromagnetic flares can be launched for a wide variety of orbital parameters.

I will introduce a new discrete transformation in quantum field theory with Z2 1-form symmetry, with some applications to boson/fermion dualities in (2+1)d.

This is based on the work https://arxiv.org/abs/1909.07383with Shu-Heng Shao (IAS).

**Please Note:** This workshop is not open to the general public, but only to active researchers.This workshop will focus on quantum aspects of black holes, focusing on applying ideas from quantum information theory.This meeting is sponsored by the "It from Qubit"collaboration and is followed by the collaboration meeting in New York City.

Very light axions are a generic prediction of string compactifications. If cosmic strings associated with these axions were produced in the early universe, they quickly approach a so-called scaling solution, such that strings persist in the sky today. I will present some remarkable signals of such strings coupled to photons. In this string background, there is a model-independent polarization rotation of CMB photons equal to $\alpha_{em}$ up to a rational number. This manifests itself as a rotation of E-modes in the CMB polarization to B-modes. The current CMB experimental sensitivity to this rotation is about 1%, with many orders of magnitude improvement expected for future experiments. I will show how measuring the undetermined rational number may shed light on the quantization of electric charge in the standard model. These strings may also be visible in strongly lensed quasar systems.

**Please Note:** This workshop is not open to the general public, but only to active researchers.This workshop will focus on quantum aspects of black holes, focusing on applying ideas from quantum information theory.This meeting is sponsored by the "It from Qubit"collaboration and is followed by the collaboration meeting in New York City.

The National Academy has recently called for the US to adopt a strategy to produce fusion electricity from a compact pilot plant by mid-century. This approach requires innovations in technology (e.g. magnet systems and power handling systems) and innovations in physics. I will introduce the key issues that challenge the current program and recent theoretical and experimental progress. I will also discuss research at PPPL to develop optimal three dimensional magnetic configurations and low cost engineering solutions for their realization.

Every astrophysically realistic simulation needs accurate initial data and in this talk I will present methods to obtain such solutions for a variety of problems. In particular I will focus on a new initial data formulation to solve the full set of Einstein equations for spacetimes that contain a black hole under general conditions. As an application I will present nonaxisymmetric, self-gravitating tori in the presence of a black hole whose spin is tilted with respect to the angular momentum of the disk. The numerical implementation of these methods is done in the context of the Compact Object CALculator (COCAL) code whose purpose is to provide initial data for any general-relativistic system.

In the second part of this talk I will address two questions: First, how one can distinguish a binary black hole undergoing a merger from a binary neutron star if the individual compact companions have masses that fall inside the so-called mass gap of 3-5 solar masses? I will show that although the ringdown phase is indistinguishable from the perturbed Kerr spacetime, the inspiral phase can lead to measurable differences. Second, whether any of the known neutron stars that exhibit ergoregions are dynamically stable? If not, can we identify any dynamically stable ergostar? The answer to these questions will have consequences to the conjecture by Komissarov that a horizon is not necessary for the energy creation of a relativistic jet.

The Cosmic Microwave Background is a unique tool to investigate the early universe and the largest structures observable in the sky. The main CMB observables such as anisotropies, polarization state and Sunyaev Zel’Dovich effect can give us a detailed view of the cosmos providing stringent constraints to the parameters of our models. To extract the information encoded in the radiation we need extremely sensitive detectors and low noise readout. Transition edge sensors and superconducting quantum interference devices are the state of the art technology for this purpose. The implementation on present and future balloon borne experiments will be introduced and discussed as well as the next generation ground experiments.

The Andromeda galaxy is the closest spiral galaxy to us. It harbors a massive dark matter halo which may span up to ∼600 kpc across and comprises ∼90% of the galaxy’s total mass. This halo size translates into a large diameter of 42 degrees on the sky for an M31–Milky Way distance of 785 kpc, but its presumably low surface brightness makes it challenging to detect with gamma-ray telescopes. Using data from the Fermi Large Area Telescope, we make a detailed study of the gamma-ray emission between 1-100 GeV towards Andromeda's outer halo, and perform an in-depth analysis of the systematic uncertainties related to the observations. In this talk, I will discuss these results and implications for dark matter.

We will prove a conjecture [1] on upper bound of asymptotic gap in dimension in unitary compact 2D CFT, proving it to be 1 using a "extremal" function [2]. The notion of asymptotic gap can be generalized to (h, \bar{h}) plane [3]. We will discuss how the extremal function used in [2] can be put into a bigger (natural) framework of an extremal problem of entire function with certain exponential growth [4]. This facilitates a generalization of construction of optimal function (within the class of Bandlimited function) and hence the optimal gap on (h, \bar{h}) plane. Reading material:[1] Baur Mukhametzhanov, Alexander Zhiboedov, *Modular Invariance, Tauberian Theorems, and Microcanonical Entropy*, arXiv: 1904.06359 [hep-th][2] Shouvik Ganguly, SP, *Bounds on density of states and spectral gap in CFT_2*, arXiv: 1905.12636 [hep-th] (in particular section 4)[3] SP, Zhengdi Sun,* Tauberian-Cardy formula with spin*, arXiv: 1910.07727 [hep-th]

[4] D. V. Gorbachev, * Extremum Problems for Entire Functions of Exponential Spherical Type*, Mathematical Notes, Vol 68, N0. 2, 2000

I will mostly be focussing on the extremal problem. More reading material on application of Tauberian theorem can be found in:

1. D. Pappadopulo, S. Rychkov, J. Espin, and R. Rattazzi, Operator product expansion convergence in conformal field theory, Physical Review D 86 no. 10, (2012) 105043.2. J. Qiao and S. Rychkov, A tauberian theorem for the conformal bootstrap, JHEP 12 (2017) 119, arXiv:1709.00008 [hep-th].3. B. Mukhametzhanov and A. Zhiboedov, Analytic euclidean bootstrap, arXiv preprint arXiv:1808.03212 (2018).4. SP, Bound on asymptotics of magnitude of three point coefficients in 2D CFT, arXiv:1906.11223 [hep-th].5. Appendix C of D. Das, S. Datta, and SP, Charged structure constants from modularity, JHEP 11 (2017) 183, arXiv:1706.04612 [hep-th].

The immune system is composed of a large number of heterogenous interacting components that collectively recognize and clear pathogens. To cover the high-dimensional molecular space of all possible threats, including those that have never been seen before, the adaptive immune system is endowed with a wide variety of receptor proteins, which are created by random cutting-and-pasting of the DNA in each cell. I will show how the rules of that process can be statistically learned from high-throughput sequencing data, and can be used to calculate its entropy and to predict accurately receptor overlap between individuals. I will then present a theoretical framework for thinking about optimal designs for enacting and encoding immune memory through the self-organisation of the repertoire.

I will discuss topological classification of gapped many-body Hamiltonians and their ground states in dimension d. In general, the problem is too hard as it includes diverse phenomena such as degenerate ground states on the torus, anyons, and fractons. There is, however, hope to fully understand short-range entangled, or "invertible" systems, which do not have the aforementioned features but may possess gapless edge modes. In the case of non-interacting fermions, the topological classification is based on K-theory. I will argue that general invertible systems are described by some homotopy spectrum (or equivalently, generalized cohomology theory). However, the exact answer is not yet known.

In its high-luminosity phase, the CERN Large Hadron Collider will produce x10 more data, while the computing power for data processing will not scale accordingly. Particle physicists need novel solutions to accomplish the scientific mission of the LHC. Deep Learning has the potential to be the game changer that could solve the problem. In this seminar, I will describe the main conceptual and technological problems that need to be addressed by 2026 and where Deep Learning could play a major role.

LOCATION:Jadwin Hall Room 303 COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200121T190000Z DTEND:20200121T203000Z SUMMARY:PCTS Special Seminar, "Physics and Energy" (Robert L. Jaffe, MIT) DESCRIPTION:Energy is a central concept in physics. Because energy is conserved, it is possible to understand the behavior of complex systems by tracing the flow of energy through them. On the other hand, we humans “consume” energy, degrading it into less useful forms, as it powers modern societies. Providing energy for the world to use in a sustainable fashion is a major, perhaps existential challenge for humankind in the 21st century. The scale and scope of the problem is enormous. The implications for Earth and human societies are profound.

Economic considerations and political decisions will be central to any attempt to address this energy challenge. However, decisions made in the absence of good scientific understanding have the potential to waste vast amounts of effort and resources and to adversely affect countless lives and large ecosystems. A clear understanding of the science of energy is essential for specialists and non-specialists alike. Physicists and our universities have an opportunity, even a responsibility to provide this understanding.

In response to this challenge, Washington Taylor and I developed a physics course for MIT undergraduates and an associated textbook — *“The Physics of Energy”* –– that focus on the sources and uses of energy, and on energy systems and the externalities associated with energy use, including climate change. After setting out the nature of the problem, I will describe the motivation for and structure of an energy-centered university physics course for students with a strong science and math background, illustrate the topics it covers, and relate some of the insights that we uncovered along the way.

Compositeness is an elegant way to address the hierarchy problem. In this talk, under broad assumption of partial compositeness and Higgs doublet as the pseudo-Nambu-Goldstone bosons, I will discuss about phenomenology of the spin-1 resonances and the top partners in CHMs and the relevance of their strong interactions in the searches at the LHC. I will also discuss about the strong multi-pole interaction as the target scenario for the precision measurement in the di-boson processes at the HL-LHC. Finally, I will briefly discuss about the universal relationship between the Higgs couplings predicted by the non-linearity and their phenomenological relevance in the future lepton colliders.

LOCATION:Jadwin Hall Room 303 COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200128T210000Z DTEND:20200128T210000Z SUMMARY:Pheno & Vino Seminar, "Soft Signals at the LHC" (Simon Knapen, Institute for Advanced Study) DESCRIPTION:The LHC is both a Higgs and B-factory, and for both particles it will likely deliver the largest data set we will see in our lifetimes. I will discuss a few examples on how we can leverage this to search for beyond the Standard Model physics. Some ideas can be implemented now, while others rely on the phase II upgrade.

LOCATION:Princeton University Jadwin Hall Room 303 COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200203T150000Z DTEND:20200203T190000Z SUMMARY:Dark Matter at Jadwin: An Informal Mini- Symposium DESCRIPTION: LOCATION: COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200203T173000Z DTEND:20200203T173000Z SUMMARY:Gravity Initiative Lunch, "Finite Size Effects on the Self-Force" (Klaountia Pasmatsiou, Case Western Reserve University) DESCRIPTION:Electromagnetic and linear gravitational radiation do not solely propagate on the null cone in 3+1 dimensions in curved spacetimes, contrary to their well-known behavior in flat spacetime. Their additional propagation inside the null cone is known as the tail effect. In the first part of the talk, I will present new results for the tail-induced electromagnetic and gravitational self-force for a test particle in orbit around a central body. This test particle will produce a signal whose tail will interact with its future worldline, thus producing a tail-induced self-force. I will show that the self force can serve as a probe of the internal structure of the central object, with possible future implications for neutron star-black hole mergers. During the second part of the talk, I will present preliminary results towards the development of the "tail electrodynamics" and the propagation of tail radiation in a weakly curved spacetime.

LOCATION:Jadwin Hall, Princeton Gravity Initiative, 4th Floor COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200203T193000Z DTEND:20200203T193000Z SUMMARY:High Energy Theory Seminar, "X-ray Search for Axions from Nearby Isolated Neutron Stars" (Ben Safdi, University of Michigan) DESCRIPTION:Axions may be produced thermally inside the cores of neutron stars (NSs), escape the stars due to their weak interactions with matter, and subsequently convert into X-rays in the magnetic fields surrounding the NSs. I will describe a hard X-ray search from 2 - 8 keV for X-rays arising from this emission mechanism from the nearby Magnificent Seven isolated NSs using archival XMM-Newton and Chandra data. This search leads to the strongest limits to-date on the product of the axion-photon and axion-nucleon couplings for axion masses below ~1e−4 eV. Moreover, I will show that an observed excess of hard X-rays from the Magnificent Seven may arise from axions, and I will discuss near-term measurements to help rule out or confirm this possibility. LOCATION:Bloomberg Lecture Hall (IAS) COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200204T210000Z DTEND:20200204T210000Z SUMMARY:Pheno & Vino Seminar, "Dynamical Friction in a Fuzzy Dark Matter Universe" (Cara Giovanetti, Princeton University) DESCRIPTION:Fuzzy Dark Matter (FDM) is a model of dark matter consisting of an ultralight scalar whose quantum mechanical nature is manifest at kiloparsec scales. As such, an object moving through an FDM halo will experience a different drag force due to dynamical friction than an object passing through a classical dark matter halo. This effect is pronounced enough that it can be observed when measuring the infall times of satellites as they spiral in towards galaxy centers. In this talk I will explore the use of analytical theory and numerical simulations to determine the magnitude of this effect. I will also apply these results to different astrophysical systems and discuss the use of dynamical friction to support or rule out FDM as a dark matter candidate.

LOCATION:Jadwin Hall Room 303 COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200206T164500Z DTEND:20200206T164500Z SUMMARY:PCTS Seminar Series: Deep Learning for Physics, "Topic #1: Understanding Machine Learning via Exactly Solvable Statistical Physics Models; Topic #2: Dynamics of Generalization in Overparameterized Neural Networks" (Speaker #1: Lenka Zdeborova; Speaker #2: Andrew Saxe, Speaker #1: CEA Scalay and CNRS; Speaker #2: Oxford University) DESCRIPTION:Please Note: The seminars are not open to the general public, but only to active researchers.

Register here for this event:

https://docs.google.com/forms/d/e/1FAIpQLScJ-BUVgJod6NGrreI26pedg8wGEyPhh3WMDskE1hIac_Yp3Q/viewform

Abstract for talk #1: The affinity between statistical physics and machine learning has long history, this is reflected even in the machine learning terminology that is in part adopted from physics. I will describe the main lines of this long-lasting friendship in the context of current theoretical challenges and open questions about deep learning. Theoretical physics often proceeds in terms of solvable synthetic models, I will describe the related line of work on solvable models of simple feed-forward neural networks. I will highlight a path forward to capture the subtle interplay between the structure of the data, the architecture of the network, and the learning algorithm.

Abstract for talk #2: What interplay of dynamics, architecture, and data make good generalization possible in overparameterized neural networks? Approaches from statistical physics have shed light on this question by considering a variety of simple limiting cases. I will describe results emerging from two simple models: deep linear neural networks and nonlinear student-teacher networks. In these models, good generalization from limited data arises from aspects of training dynamics and initialization. Finally, I will briefly tour open problems facing practitioners that seem amenable to analysis with similar methods.

Each talk will be preceded with lunch at 11:45 am. The talks will be held from 12:25-1:30 pm and from 2:00 - 3:00 pm.

URL:http://pcts.princeton.edu/programs/current/deep-learning-for-physics-seminar-series/121 END:VEVENT BEGIN:VEVENT UID: DTSTART:20200207T184500Z DTEND:20200207T184500Z SUMMARY:High Energy Theory Seminar, "Three Avatars of Mock Modularity" (Atish Dabholkar, Abdus Salam ICTP, Trieste) DESCRIPTION:Mock theta functions were introduced by Ramanujan in his famous last letter to Hardy in 1920 but were properly understood only recently with the work of Zwegers in 2002. I will describe three manifestations of this apparently exotic mathematics in three important physical contexts of holography, topology and duality where mock modularity has come to play in important role.

In particular, I will derive a holomorphic anomaly equation for the indexed partition function of a two-dimensional CFT2 dual to AdS3 that counts the black hole degeneracies, and for Vafa-Witten partition function for twisted four dimensional N=4 super Yang-Mills theory on CP2 for the gauge group SO(3) that counts instantons. The holomorphic kernel of this equation is not modular but `mock modular’ and one obtains correct modular properties only after including certain `anomalous’ nonholomorphic boundary contributions. This phenomenon can be related to the holomorphic anomaly of the elliptic genus of a two-dimensional noncompact supersymmetric sigma model, and in a simpler context of quantum mechanics to the Atiyah-Patodi-Singer eta invariant.

Mock modularity is thus essential to exhibit modular symmetries expected from the AdS3/CFT2 holographic equivalence in quantum gravity and the S-duality symmetry of four-dimensional quantum gauge theories.

LOCATION:407 Jadwin Hall, 4th Floor, PCTS Seminar Room COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200210T173000Z DTEND:20200210T173000Z SUMMARY:Gravity Initiative Lunch, "Studying Neutron Stars with Gravitational Waves" (Katerina Chatziioannou, CCA) DESCRIPTION:Neutron stars, the most dense astrophysical bodies we know of, are at the heart of many interesting astrophysical phenomena from their birth in supernova explosions to their deaths in collisions with other dense objects. Even though we have been witnessing the births of neutron stars in the night (or even day!) sky for thousands of years, the collision of two neutron stars was detected for the first time only two years ago through gravitational waves.

In this talk I will discuss what insights the detected signal, GW170817, has offered about the properties of astrophysical neutron stars and how it compares to other recent probes of neutron star matter such as NICER. I will also discuss what we expect to discover in the next few years about the properties of matter that is more dense than the nuclei everyday atoms are made of.

LOCATION:Jadwin Hall, Princeton Gravity Initiative, 4th Floor COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200210T193000Z DTEND:20200210T193000Z SUMMARY:High Energy Theory Seminar, "An Effective Field Theory of Quantum Black Hole Horizons" (Walter Goldberger, Yale University) DESCRIPTION:I develop an effective theory which describes black holes with quantum mechanical horizons that is valid at scales long compared to the Schwarzschild radius but short compared to the lifetime of the black hole. The formalism allows one to calculate the quantum mechanical effects in scattering processes involving black hole asymptotic states. The EFT Wightman functions which describe Hawking radiation in the Unruh vacuum are not Planck suppressed and are actually enhanced relative to those in the Boulware vacuum, for which such radiation is absent. We elaborate on this point showing how the non-Planck suppressed effects of Hawking radiation cancel in classical observables. Applications to inelastic gravitational scattering of point particles off quantum black holes will be briefly discussed. LOCATION:Bloomberg Lecture Hall (IAS) COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200211T210000Z DTEND:20200211T210000Z SUMMARY:Pheno & Vino Seminar, "Direct Detection Searches for Fuzzy Dark Matter and Ultra Low Mass Axions at Princeton" (William Terrano, Princeton University) DESCRIPTION:I will discuss experimental prospects for directly detecting ultra-low-mass dark matter, including the interesting “Fuzzy” dark matter scenario. I will describe experiments which are ongoing here at Princeton, and the challenges associated with them. I will also present the results we have thus far, and the prospects for future improvements.

LOCATION:Princeton University Jadwin Hall Room 303 COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200213T210000Z DTEND:20200213T210000Z SUMMARY:Hamilton Colloquium Series, "The Physics of Collective Cell Migration" (Ricard Alert, Princeton University) DESCRIPTION:Cells in our body move in groups during development, wound healing, and tumor spreading. Bacterial cells also coordinate their motion to aggregate into biofilms, to feed cooperatively, and to form fruiting bodies. All these collective movements rely on physical mechanisms involving cell-generated propulsion forces and both mechanical and biochemical interactions between cells. In the first part of the talk, I will review how cell-cell interactions lead to the emergence of collective phenomena in migrating cell groups. These phenomena include internally-driven fluid-solid and wetting transitions, hydrodynamic instabilities, as well as the appearance of orientational order, spontaneous flows, and mechanical waves even in the absence of inertial effects. I will illustrate how the quest for understanding collective cell migration has stimulated the development of active-matter physics — a new branch of non-equilibrium soft-matter physics. In the second part of the talk, I will present our studies on colonies of the soil bacterium *Myxococcus xanthus*. When the elongated and motile bacterial cells are densely packed, they align with neighboring cells and form an active liquid crystal. I will show that topological defects of the nematic cell alignment lead to the formation of new layers of cells, which triggers the growth of fruiting bodies in the bacterial colony.

Reparametrization modes provide a way of describing universal physics of energy-momentum exchanges in CFTs. Drawing inspiration from effective field theory methods and the SYK model, I will argue that this perspective offers a useful computational and conceptual framework. For example, stress tensor contributions to conformal blocks can be systematically organized in terms of reparametrization mode exchanges, thus leading to a simple and efficient diagrammatic perturbation theory at large central charge. To illustrate this method, I will discuss some known stress tensor conformal blocks in various dimensions, and will also present a new result regarding the six-point "identity block" in 2d CFTs. I will also mention an application to thermal physics in higher dimensions and argue that the theory of reparametrization modes provides useful intuition for the physics underlying quantum chaos in Rindler space.

LOCATION:Bloomberg Lecture Hall (IAS) COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200217T130000Z DTEND:20200218T220000Z SUMMARY:PCTS Workshop Structure-Preserving Geometric Discretization of Physical Systems DESCRIPTION:Registration at: https://docs.google.com/forms/d/e/1FAIpQLSeHnBCTiEdc9ZqogazfBRc6nhFJKadRUiXwjdJyrBKhjGk2RQ/viewform

http://pcts.princeton.edu/programs/current/structure-preserving-geometric-discretization-of-physical-systems/119

Topics:

Structure-preserving algorithms, Geometric integration, Geometric particle-in-cell methods, Symmetries in lattice quantum field theories

Program Organizers:

Hong Qin, Clarence Rowley, Nathaniel Fisch, and Melvin Leok

Program Committee:

Joshua Burby, Nathaniel Fisch, Arieh Iserles, Melvin Leok, Philip Morrison, Hong Qin, Clarence Rowley, and Eric Sonnendrücker

Confirmed Speakers:

• Silas Beane (Univ. Washington)

• Josh Burby (LANL)

• Elena Celledoni (Norwegian Univ. Sci. & Tech.)

• Zohreh Davoudi (Univ. Maryland)

• Evan Gawlik (Univ. Hawaii)

• Alexander Glasser (Princeton)

• Shi Jin (Shanghai Jiaotong Univ.)

• Michael Kraus (IPP Max-Planck)

• Klas Modin (Chalmers)

• Yuan Shi (LLNL)

• Ari Stern (Washington Univ.)

• Tomasz Tyranowski (IPP Max-Planck)

• Jianyuan Xiao (Univ. Sci. & Tech. China)

Hot spots, or plasmoids, formed due to magnetic reconnection in thin current sheets are conjectured to power frequent bright X-ray and near-infrared flares from supermassive black holes, like Sgr A* in the center of our Galaxy. It is of yet unclear how, where, and when thin current sheets form in black hole accretion flows, and whether magnetic reconnection in such sheets is capable of producing highly energetic plasmoids. In this talk I will show general relativistic resistive magnetohydrodynamics models of magnetic reconnection and associated plasmoid formation in a wide range of accretion flows. I will show that plasmoids are a ubiquitous feature of accretion flows regardless of the magnetic field geometry and the spin of the black hole. The location of the current sheets, how frequently they form, and typical size of the largest plasmoids do depend strongly on the magnetic field geometry. In all cases we observe plasmoids forming close to the event horizon within 5 to 10 Schwarzschild radii, after which the they grow to macroscopic scales and advect along the jet boundary or into the disk. We determine the typical reconnection rate, the Ohmic heating, and the occurence of non-ideal electric fields responsible for particle acceleration. We also show that an explicit resistivity allows for converged numerical solutions, such that the electromagnetic energy density evolution and dissipation is independent of the grid resolution and numerical heating is negligible for the extreme resolutions we considered.

LOCATION:Jadwin Hall, Princeton Gravity Initiative, 4th Floor COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200218T210000Z DTEND:20200218T210000Z SUMMARY:Pheno & Vino Seminar, "Uncovering Dark Matter with Compact Objects and Automatic Differentiation" (Christoph Weigner, University of Amsterdam) DESCRIPTION:The nature of dark matter (DM) in the Universe remains one of the great open questions of particle astrophysics and cosmology today. The WIMP (weakly interacting massive particle) DM paradigm has fallen, leaving us with a wide range of possible DM models and signatures. New methods and ideas are required to efficiently progress. I will discuss ongoing searches for axion DM signatures using radio observations of neutron stars, and discuss the potential role of black holes and gravitational waves. I will furthermore demonstrate how machine learning technology like automatic differentiation and deep universal probabilistic programming can significantly improve the analysis of astrophysical data. As application I will present preliminary results for the analysis of strongly lensed images.

LOCATION:Jadwin Hall Room 303 COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200219T130000Z DTEND:20200219T230000Z SUMMARY:PCTS Workshop, "Large N Theories and Strings: Conformal, Confining, and Holographic" DESCRIPTION:**Organizers: Nathan Benjamin, Simone Giombi, Victor Gorbenko, Shota Komatsu, Silviu Pufu, Xinan Zhou**In recent years, there has been much interesting progress from disparate subfields of high energy physics, all under the unifying theme of theories with a large number of degrees of freedom. This includes strings in confining gauge theories, conformal field theories, quantum gravity, and the gauge/string dualities. The purpose of this workshop is to bring together experts in those fields to revisit and shed new lights on the original idea of theories of large N. **Please Note: This workshop is not open to the general public, but only to active researchers.**

**Organizers: Nathan Benjamin, Simone Giombi, Victor Gorbenko, Shota Komatsu, Silviu Pufu, Xinan Zhou**In recent years, there has been much interesting progress from disparate subfields of high energy physics, all under the unifying theme of theories with a large number of degrees of freedom. This includes strings in confining gauge theories, conformal field theories, quantum gravity, and the gauge/string dualities. The purpose of this workshop is to bring together experts in those fields to revisit and shed new lights on the original idea of theories of large N. **Please Note: This workshop is not open to the general public, but only to active researchers.**

The AdS/CFT correspondence maps correlators of local operators in a conformal field theory to scattering amplitudes in a gravitational/string theory on curved space-time. The study of such amplitudes is incredibly hard and has mostly been done in a certain classical limit. We show how modern analytic bootstrap techniques allow us to go much beyond that.

LOCATION:Jadwin Hall Room A10 COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200221T130000Z DTEND:20200221T230000Z SUMMARY:PCTS Workshop, "Large N Theories and Strings: Conformal, Confining, and Holographic" DESCRIPTION:**Organizers: Nathan Benjamin, Simone Giombi, Victor Gorbenko, Shota Komatsu, Silviu Pufu, Xinan Zhou**In recent years, there has been much interesting progress from disparate subfields of high energy physics, all under the unifying theme of theories with a large number of degrees of freedom. This includes strings in confining gauge theories, conformal field theories, quantum gravity, and the gauge/string dualities. The purpose of this workshop is to bring together experts in those fields to revisit and shed new lights on the original idea of theories of large N. **Please Note: This workshop is not open to the general public, but only to active researchers.**

**Organizers: Nathan Benjamin, Simone Giombi, Victor Gorbenko, Shota Komatsu, Silviu Pufu, Xinan Zhou**In recent years, there has been much interesting progress from disparate subfields of high energy physics, all under the unifying theme of theories with a large number of degrees of freedom. This includes strings in confining gauge theories, conformal field theories, quantum gravity, and the gauge/string dualities. The purpose of this workshop is to bring together experts in those fields to revisit and shed new lights on the original idea of theories of large N. **Please Note: This workshop is not open to the general public, but only to active researchers.**

I discuss the possibility that the ''dark energy'' that drives the accelerated expansion of the universe arises not from a conventional cosmological constant term in the gravitational action, but rather from a frame-dependent but Weyl scaling invariant action term. This action mimics the standard cosmological action in an unperturbed Friedmann-Robertson-Walker (FRW) cosmology, but has novel consequences both for black hole horizons and, the focus of this talk, for perturbations around the FRW solution. I discuss motivations for a Weyl invariant cosmological action, new insights it would give on old problems, and implications for the recently much discussed ''Hubble Tension''. The talk keeps technicalities to a minimum, requiring only a basic knowledge of FRW cosmology and ordinary differential equations, and concludes with a list of problems for further study, some of which could be undergraduate paper or thesis topics.

LOCATION:Jadwin Hall, Princeton Gravity Initiative, 4th Floor COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200224T193000Z DTEND:20200224T193000Z SUMMARY:High Energy Theory Seminar, "Conformal Fishnet Theory" (Vladimir Kazakov, Ecole Normale Supérieure) DESCRIPTION:I will review the proprieties and recent results for conformal fishnet theory (FCFT) which was proposed by O.Gurdogan and myself as a special double scaling limit of gamma-deformed N=4 SYM theory. FCFT, in its simplest, bi-scalar version, is a UV finite strongly coupled 4-dimensionl logarithmic CFT dominated by planar fishnet Feynman graphs (of the shape of regular square lattice). FCFT inherits the planar integrability of N=4 SYM which becomes manifest in this case: the fishnet graphs can be mapped on the SO(2,4) integrable spin chain (A.Zamolodchikov 1980). The D-dimensional generalization of FCFT, with SO(2,D) conformal symmetry can be also provided. A remarkable property of FCFT is the possibility of spontaneous symmetry breaking, due to the flat vacua which are not lifted by quantum corrections. I will also discuss the exact computation of certain anomalous dimensions and 4-point correlators, and of related fishnet Feynman graphs (of "wheel" or "spiral" type), using the quantum integrability tools: asymptotic and thermodynamic Bethe ansatz and quantum spectral curve of N=4 SYM. LOCATION:Bloomberg Lecture Hall (IAS) COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200225T210000Z DTEND:20200225T210000Z SUMMARY:Pheno & Vino Seminar, "The Higgs Effective Theory is a Black Hole" (Timothy Cohen, University of Oregon) DESCRIPTION:Treating the Standard Model as an Effective Field Theory (EFT) yields a general framework for exploring deviations in observables that probe the indirect effects of new particles. Two treatments are typically discussed --- Higgs EFT (HEFT) and Standard Model EFT (SMEFT) --- my goal in this talk is to compare and contrast them. The key difference between them is that HEFT is formulated assuming electroweak symmetry is broken such that the physical Higgs boson excitation and the Goldstone bosons are treated as independent objects. On the other hand, SMEFT is set in the electroweak symmetric background and utilizes the complete Higgs doublet as a building block. I will argue that in practice when one works with a finite number of EFT operators, HEFT has superior convergence properties for exploring the impact of new particles whose masses are near or below the weak scale. I will then turn to the question of when one is *required* to match onto HEFT, by exploring the singularity structure of the Higgs manifold. Many points will be clarified by relying on a variety of physical examples.

I will describe a formalism for treating Quantum Field Theories in de Sitter space, which, in particular, resolves the issue of infrared divergences often present in perturbation theory.

LOCATION:Bloomberg Lecture Hall (IAS) COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200302T173000Z DTEND:20200302T173000Z SUMMARY:Gravity Initiative Lunch, "The Breakdown of Weak Null Singularities Inside Black Holes" (Maxime Van De Moortel, Princeton University) DESCRIPTION:The characterization of singularities inside black holes is a fundamental problem in General Relativity. While the celebrated “mass inflation” scenario suggests that a weakly *singular* Cauchy horizon forms inside generic black holes (near time-like infinity), the global structure of the black hole interior boundary has largely remained unexplored. I will present my recent proof that, in the context of the spherical collapse of a charged scalar field, the weakly singular Cauchy horizon breaks down in finite retarded time and gives way to either a r = 0 “crushing type” singularity, or a locally naked singularity emanating from the center of symmetry.

LOCATION:Jadwin Hall, Princeton Gravity Initiative, 4th Floor COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200303T210000Z DTEND:20200303T210000Z SUMMARY:Pheno & Vino Seminar, "The 2 to 3 Frontier in NNLO LHC Calculations" (Alexander Mitov, Cavendish Lab, Cambridge) DESCRIPTION:For the last 5 years or so, there has been a major effort towards the calculation of two-loop 5-point QCD amplitudes and their corresponding LHC cross-sections at NNLO. Very recently, the first such calculation - 3-photon production - was completed [arXiv:1911.00479]. I will explain the novel features, and lessons learned, in regard to 5-point two-loop QCD amplitudes. I will also present a detailed comparison of the new NNLO predictions for 3-photon production with existing LHC measurements. Such a comparison is of particular interest given the discrepancy between NLO predictions and data. This calculation represents a stepping stone for tackling another LHC milestone: 3-jet production in NNLO QCD. An update on the ongoing 3-jet calculation will be given. The seminar should be of interest to both theorists and LHC experimentalists.

LOCATION:Jadwin Hall Room 303 COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200306T184500Z DTEND:20200306T184500Z SUMMARY:High Energy Theory Seminar, "Modular Invariance in Superstring Theory from N=4 Super-Yang-Mills" (Silviu Pufu, Princeton University) DESCRIPTION:In this talk, I will first review some of the recent progress on computing holographic correlators using analytic bootstrap techniques combined with supersymmetric localization, focusing on the case of the N = 4 super-Yang-Mills theory. From taking a certain flat space limit of the holographic correlators, one can obtain scattering amplitudes of gravitons in string theory, and one can then reproduce some of the known results for these scattering amplitudes. In particular, from instanton effects in the N=4 SYM theory, I will explain how to reproduce the non-holomorphic Eisenstein series known to appear in type IIB string theory scattering amplitudes.

LOCATION:Princeton University, 407 Jadwin Hall, PCTS Seminar Room COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200309T163000Z DTEND:20200309T163000Z SUMMARY:Gravity Initiative Lunch, "The Quasi-Local Penrose Inequality and the Hoop Conjecture" (Martin Lesourd, Harvard BHI) DESCRIPTION:The Spacetime Inequality of Penrose 1972 says that any slice in any black hole spacetime, the ADM mass of the slice is bounded below by the area of cuts with the event horizon. (Its quasi-local version is a refinement involving quasi-local notions of mass and energy). The Hoop Conjecture proposed by Thorne 1972 says that black holes form when the quasi-local mass M associated with some region of some characteristic length C satisfies ''M > const. C''. These conjectures are open in full generality and I will present some recent progress which proves them in a certain setting. This is joint with S.T. Yau and A. Alaee.

LOCATION:Princeton University, Jadwin Hall, Princeton Gravity Initiative, 4th Floor COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200310T200000Z DTEND:20200310T200000Z SUMMARY:Pheno & Vino Seminar, "Quantum Computing and Machine Learning in High Energy Data Analysis" (Prasnth Shyamsundar, University of Florida) DESCRIPTION:Recently there has been a growing interest in the application of quantum computing and machine learning in many scientific disciplines, including high energy physics. In the first half of this talk, we will look at a novel quantum computing based technique to search for unmodeled deviations from a simulated expectation in high-dimensional collider data. In the second half, we will look at some ways in which the goals of machine learning, as it is used currently in analyses, are not perfectly aligned with the physics goals of the analyses. We will also look at ways of rectifying the demonstrated misalignments.

LOCATION:Jadwin Hall Room 303 COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200316T183000Z DTEND:20200316T183000Z SUMMARY:High Energy Theory Seminar, "Covariant Phase Space with Boundaries" (Daniel Harlow, Massachusetts Institute of Technology) DESCRIPTION:To connect to the HET Seminar via Zoom, please do the following:

1 - If you have Zoom installed on your device, enter the following meeting ID: 434238729, click Join Meeting.

2 - If you do not have Zoom installed, click the following link to download and install: https://theias.zoom.us/j/434238729

3 - Once installed, click the very same link to connect to the meeting.

Abstract: The Hamiltonian formulation of mechanics has many advantages, but its standard presentation destroys manifest covariance. This can be avoided by using the "covariant phase formalism" of Iyer and Wald, but until recently this formalism has suffered from several ambiguities related to boundary terms and total derivatives. In this talk I will present a new version of the formalism which incorporates boundary effects from the beginning. This eliminates all ambiguities, and leads to an algorithmic procedure for covariantly constracting the phase space and Hamiltonian of any Lagrangian field theory. It also allows us to confirm that the Poisson bracket in covariant phase space is indeed equivalent to an old proposal of Peierls for computing Poisson brackets covariantly. Along the way I'll illustrate the formalism using various examples. Based on work with Jie-qiang Wu.

LOCATION:https://theias.zoom.us/j/434238729 COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200320T174500Z DTEND:20200320T174500Z SUMMARY:High Energy Theory Seminar, "How to See Everything in the Entanglement Wedge" (Adam Levine, Member, School of Natural Sciences, Institute for Advanced Study) DESCRIPTION:To connect to the HET Seminar via Zoom, please do the following:

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Abstract: We will describe work in progress in which we argue that a generalization of the procedure developed by Gao-Jafferis-Wall can allow one to see the entirety of the entanglement wedge. Gao-Jafferis-Wall demonstrated that one can see excitations behind the horizon by deforming the boundary Hamiltonian using a non-local operator. We will argue in a simple class of examples that deforming the boundary Hamiltonian by a specific modular Hamiltonian can allow one to see (almost) everything in the entanglement wedge. Time permitting, we may comment on connections to previous proposals for bulk reconstruction and possible future directions.

LOCATION:via ZOOM COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200324T200000Z DTEND:20200324T200000Z SUMMARY:Pheno & Vino Seminar, "Direct Detection Experiments in the Gaia Era" (JiJi Fan, Brown University) DESCRIPTION:Please use this link to sign into the remote talk via ZOOM: http://bit.ly/phenoandvino

The advent of the Gaia era has led to potentially revolutionary understanding of dark matter dynamics in our galaxy, which has important consequences for direct detection experiments. In this talk, I will discuss the effects of various dark matter substructures inferred from the Gaia data on possible direct detection signals at next-generation experiments. In particular, I will focus on the implications of the so-called Gaia sausage for the dark matter-nuclear interactions, as well as the unique modulation signatures of several possible streams associated with dark matter-electron interactions.

LOCATION:via ZOOM COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200327T174500Z DTEND:20200327T174500Z SUMMARY:High Energy Theory Seminar, "Solving Random Matrix Models with Positivity" (Henry Lin, Princeton University) DESCRIPTION:To connect to the HET Seminar via Zoom, please do the following:

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Abstract: A new approach to solving random matrix models directly in the large N limit is developed. First, a set of numerical values for some low-pt correlation functions is guessed. The large N loop equations are then used to generate values of higher-pt correlation functions based on this guess. Then one tests whether these higher-pt functions are consistent with positivity requirements, e.g., tr M^{2k} > 0. If not, the guessed values are systematically ruled out. In this way, one can constrain the correlation functions of random matrices to a tiny subregion which contains (and perhaps converges to) the true solution. This approach is tested on single and multi-matrix models and handily reproduces known solutions. It also produces strong results for multi-matrix models which are not believed to be solvable. A tantalizing possibility is that this method could be used to search for new critical points, or string worldsheet theories.

LOCATION:via ZOOM COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200330T163000Z DTEND:20200330T163000Z SUMMARY:Gravity Initiative Lunch - CANCELED, "TBA" (Matthew Heydeman, Princeton University) DESCRIPTION: LOCATION:Jadwin Hall, Princeton Gravity Initiative, 4th Floor COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200330T183000Z DTEND:20200330T183000Z SUMMARY:High Energy Theory Seminar, "Geometry and 5d N=1 QFTs" (Lakshya Bhardwaj, Harvard University) DESCRIPTION:

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**Abstract:** I will explain that a geometric theory built upon the theory of complex surfaces can be used to understand wide variety of phenomena in five-dimensional supersymmetric theories, which includes the following:

- Classification of 5d superconformal field theories (SCFTs).
- Enhanced flavor symmetries of 5d SCFTs.
- 5d N=1 gauge theory descriptions of 5d and 6d SCFTs.
- Dualities between 5d N=1 gauge theories.
- T-dualities between 6d N=(1,0) little string theories.

This relationship between geometry and 5d theories is based on M-theory and F-theory compactifications.

LOCATION:via ZOOM COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200403T174500Z DTEND:20200403T174500Z SUMMARY:Princeton University High Energy Theory Seminar, "The Supersymmetric Cardy Formula from Effective Actions" (Martin Fluder, Princeton University) DESCRIPTION:**To connect to the HET Seminar via Zoom, please do the following:**

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**Abstract:** In this talk I will discuss supersymmetric Cardy formulae in d=4 and d=6. These formulae govern the universal behavior in the high-temperature regime of supersymmetric partition functions — or, in the case of the superconformal index, they govern the high-energy asymptotics of SUSY operators at large energy. I will outline the proof of the Cardy formulae for theories with moduli spaces of vacua, which relies on an effective supersymmetric Chern-Simons action in d-1 dimensions. I will argue that this effective action is universal and intimately related to perturbative as well as global gravitational anomalies. Finally, I will discuss some immediate consequences of our results and briefly compare and distinguish our results to other proposed Cardy formulas.

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**Abstract:** Quantum chaotic dynamics is associated to diverse physical phenomena and signatures. In this talk, we describe progress in building effective theories for three of these: the butterfly effect, the pole skipping phenomenon, and thermalization through the lens of entanglement entropy. We uncover their interplay by showing that the butterfly velocity plays an important role in all three manifestations of chaos. The discussion is informed by results from AdS/CFT and from models of SYK type.

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Via Web Browser / Zoom App: https://unige.zoom.us/j/747717345

Meeting ID: 747 717 345

**Abstract:** The WKB method has played a fundamental role in the development of quantum mechanics. In the 1980s and 1990s, and largely under the influence of Ecalle’s theory of resurgence, it was upgraded to the exact (or complex) WKB method. More recently, developments in supersymmetric gauge theory and string theory have provided a new perspective on this venerable subject. In this talk I will review the basic ingredients of the exact WKB method and present new results inspired by gauge theory/string theory. I will show in particular that the work of Gaiotto-Moore-Neitzke on BPS states provides an elegant solution of the exact WKB method as applied to arbitrary polynomial potentials. I will also discuss some open problems in the subject.

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Abstract: In this talk, I will lay out a set of efficient rules for computing d-dimensional global conformal blocks in arbitrary Lorentz representations in the context of the embedding space operator product expansion (OPE) formalism. With these rules in place, the general procedure for determining all possible conformal blocks is reduced to (1) identifying the relevant group theoretic quantities and (2) applying the conformal rules to obtain the blocks. The rules represent a systematic prescription for computing the blocks in a convenient mixed OPE-three-point- function basis as well as a set of rotation matrices, which are necessary to translate these blocks to the pure three-point function basis relevant for the conformal bootstrap. I will start by tracing their origin by describing some of the essential ingredients present in the formalism that naturally give rise to these rules. I will then map out the derivation of the rules, first outlining the general algorithm for the rotation matrices and then proceeding to the conformal blocks. Along the way, l will introduce a convenient diagrammatic notation (somewhat reminiscent of Feynman diagrams), which serves to encode parts of the computation in a compact form. Finally, I will treat several interesting examples to demonstrate the application of these rules in practice.

LOCATION:via ZOOM COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200414T190000Z DTEND:20200414T190000Z SUMMARY:Rutgers NHETC Seminar, "TBA" (Clay Cordova, University of Chicago) DESCRIPTION: LOCATION:via web conference - TBA COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200417T174500Z DTEND:20200417T174500Z SUMMARY:IAS High Energy Theory Seminar, "TBA" (Raghu Mahajan, Member, School of Natural Sciences, Institute for Advanced Study) DESCRIPTION:To connect to the HET Seminar via Zoom, please do the following:

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In this talk I will revisit and connect various non-perturbative approaches to the quantization of the Seiberg-Witten curves. I will focus on the explicit example of N = 2, SU(2) super Yang–Mills theory, which is closely related to the modified Mathieu operator. I will then show how we can obtain a closed formula for the Fredholm determinant and the spectral traces of this operator.

LOCATION:via web conference - TBA COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200428T200000Z DTEND:20200428T200000Z SUMMARY:Pheno & Vino Seminar, "Statistical Inference of Dark Matter Substructure with Weak and Strong Gravitational Lensing" (Siddharth Mishra-Sharma, New York University) DESCRIPTION:I will describe two separate methods to statistically infer the properties of dark matter substructure using, in turn, (astrometric) weak and strong lensing observations. In the first part of the talk, I will describe how the motion of dark matter subhalos in the Milky Way induces a correlated pattern of motions in background celestial objects---known as astrometric weak lensing---and how global signatures of these correlations can be measured. These measurement can be used to statistically infer the underlying nature of substructure, and I will show how this can be practically achieved with future astrometric surveys and/or radio telescopes such as WFIRST and the SKA. Next, I will describe a novel method to disentangle the collective imprint of dark matter substructure on extended arcs in galaxy-galaxy strong lensing systems using likelihood-free (or simulation-based) inference techniques. This method uses neural networks to directly estimate the likelihood ratios associated with population-level parameters characterizing substructure within lensing systems. I will show how this method can provide an efficient and principled way to mine the large sample of strong lenses that will be imaged by future surveys like LSST and Euclid to look for signatures of dark matter substructure. I will emphasize how the statistical inference of substructure using these techniques can be used to stress-test the Cold Dark Matter paradigm and probe alternative scenarios such as scalar field dark matter and enhanced primordial fluctuations.

LOCATION:Jadwin Hall Room 303 COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200501T174500Z DTEND:20200501T174500Z SUMMARY:High Energy Theory Seminar, "TBA" (Ying Zhao, Member, School of Natural Sciences, Institute for Advanced Study) DESCRIPTION:To connect to the HET Seminar via Zoom, please do the following:

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The workshop program will be posted soon. You can register for the workshop here:

https://docs.google.com/forms/d/e/1FAIpQLSfSZ8TGuAvVsoENQu5nvRbo8aEvoGn37OyNybJclACXwNgi6Q/viewform

Speakers

- Fabio Antonini, Cardiff University
- Manuela Campanelli, RIT
- Julie Comerford, University of Colorado-Boulder
- Suvi Gezari,University of Maryland
- Steffan Gillessen, MAX PLANCK INSTITUTE (MPE)
- Yuri Levin, Columbia University and Flat Iron Institute, CCA
- Xin Liu, University of Illinois
- Chung-Pei Ma, UC Berkeley
- Brian Metzger, Columbia university
- Diego Munoz, Northwestern University (CIERA)
- Smadar Naoz, UCLA
- Michael Tremmel, Yale
- Karina Voggel, Strasbourg Observatory, France
- Marta Volonteri, Institut d’Astrophysique de Paris (IAP)

Organizing committee: Fani Dosopoulou, Jeremy Goodman, Jenny Greene, and James Stone

LOCATION:Princeton University, 407 Jadwin Hall, PCTS Seminar Room COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200505T120000Z DTEND:20200505T130000Z SUMMARY:Joint Gravity Initiative / PCTS Workshop, "Exploring Supermassive Black Holes" DESCRIPTION:Speakers

Fabio Antonini, Cardiff University

Manuela Campanelli, RIT

Julie Comerford, University of Colorado-Boulder

Suvi Gezari,University of Maryland

Steffan Gillessen, MAX PLANCK INSTITUTE (MPE)

Yuri Levin, Columbia University and Flat Iron Institute, CCA

Xin Liu, University of Illinois

Chung-Pei Ma, UC Berkeley

Brian Metzger, Columbia university

Diego Munoz, Northwestern University (CIERA)

Smadar Naoz, UCLA

Michael Tremmel, Yale

Karina Voggel, Strasbourg Observatory, France

Marta Volonteri, Institut d’Astrophysique de Paris (IAP)

Organizing committee: Fani Dosopoulou, Jeremy Goodman, Jenny Greene, and James Stone

The workshop program will be posted soon. You can register for the workshop here:

https://docs.google.com/forms/d/e/1FAIpQLSfSZ8TGuAvVsoENQu5nvRbo8aEvoGn37OyNybJclACXwNgi6Q/viewform

Quantum field theory (QFT) works remarkably well for making theoretical predictions in collider scattering experiments. One of the fundamental objects in these calculations, the scattering matrix (S-matrix), is inspired by a well defined operator in non-relativistic quantum mechanics, but is plagued with both ultraviolet (UV) and infrared (IR) divergences in QFT. The UV divergences are now understood through the program of renormalization, but IR divergences remain an active area of research. We have explored three approaches to ameliorate the problem of IR divergences, which will all be discussed in this talk: i) The cross section method, ii) modification of the S-matrix, and iii) the coherent state formalism. The minimal set of processes required for a finite cross section as dictated by the KLN theorem will be elaborated on, along with examining a new approach based on factorization to define finite S-matrix elements in theories with massless particles and its connection to coherent states.

LOCATION:via web conference - TBA COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200506T120000Z DTEND:20200506T120000Z SUMMARY:Joint Princeton Gravity Initiative / PCTS Workshop, "Exploring Supermassive Black Holes" DESCRIPTION:The workshop program will be posted soon. You can register for the workshop here:

https://docs.google.com/forms/d/e/1FAIpQLSfSZ8TGuAvVsoENQu5nvRbo8aEvoGn37OyNybJclACXwNgi6Q/viewform

Speakers

- Fabio Antonini, Cardiff University
- Manuela Campanelli, RIT
- Julie Comerford, University of Colorado-Boulder
- Suvi Gezari,University of Maryland
- Steffan Gillessen, MAX PLANCK INSTITUTE (MPE)
- Yuri Levin, Columbia University and Flat Iron Institute, CCA
- Xin Liu, University of Illinois
- Chung-Pei Ma, UC Berkeley
- Brian Metzger, Columbia university
- Diego Munoz, Northwestern University (CIERA)
- Smadar Naoz, UCLA
- Michael Tremmel, Yale
- Karina Voggel, Strasbourg Observatory, France
- Marta Volonteri, Institut d’Astrophysique de Paris (IAP)

Organizing committee: Fani Dosopoulou, Jeremy Goodman, Jenny Greene, and James Stone

LOCATION:Princeton University, 407 Jadwin Hall, PCTS Seminar Room COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200512T190000Z DTEND:20200512T190000Z SUMMARY:Rutgers NHETC Seminar, "TBA" (Aswin Balasubramanian, Rutgers University) DESCRIPTION: LOCATION:via web conference - TBA COMMENT: URL: END:VEVENT BEGIN:VEVENT UID: DTSTART:20200713T110000Z DTEND:20200714T000000Z SUMMARY:PiTP 2020 DESCRIPTION: