Keisuke Harigaya's webpage

I am a theoritical particle physicist. I am paticularly interested in the strong CP problem, axion cosmology, dark matter, grand unification, electroweak symmetry breaking and inflation.

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Features on my recent works

Cosmology of the QCD Axion

It is expected that the CP symmetry is broken in the strong interaction. Non-observation of the neutron electric dipole moment shows that the CP violation is extremely small. The QCD axion explains the smallness of the CP violation. The QCD axion is also a good dark matter candidate. I have been studying cosmological evolution of the QCD axion.

axiogenesis

Axiogenesis

The rotation of the QCD axion field (black marble) around its potential during the earliest moments of the universe can generate the excess of matter (colored marbles) over antimatter, allowing galaxies and humans to exist in an otherwise-empty universe.

parametric resonance

QCD Axion Dark Matter with a Small Decay Constant
QCD Axion Dark Matter from a Late Time Phase Transition

The QCD axion can be abundantly produced by parametric resonance in the early universe. As a result the QCD axion can explain the observed dark matter abundance in the mass range where the conventional mechanisms struggle. The QCD axion produced in this way may have non-negligible velocity and change the stroncture formation in the early universe.

Flat Higgs potential at high enregy scales and Higgs Parity

It is known that the Higgs potential becomes flat at very high enery scales. I and my collaborators have found a new explanation to the flatness of the potential based on a symmetry which we call Higgs Parity, and its spontaneous breaking. The symmetry breaking scale is predicted as a function of the standard model parameters such as the Higgs mass, the top quark mass and the gauge coupling constants.

gauge coupling unification

Implications of Higgs Discovery for the Strong CP Problem and Unification
Higgs Parity Grand Unification

Higgs Parity leads to a new scheme of gauge coupling unification and a solution to the strong CP problem. Successful gauge coupling unification requires that the Higgs Parity symmetry braking scale is in a certain range, and hence the standard model parameters are predicted.

dark matter vs mtop

Higgs Parity, Strong CP, and Dark Matter

A class of Higgs Parity predicts a dark matter candidate, whose mass is proportional to the Higgs Parity symmetry breaking scale. Higgs Parity constrains the structure of the theory, so that the interaction strength of the dark matter candidate with nucleons are fixed. As a result, the dark matter direct detection rate is predicted as a function of the standard model parameters.