Research & Publications

Dark Matter

Dark matter accounts for about one-quarter of the total energy density of the universe. Its microscopic nature is still one of the central open problems in both particle physics and cosmology.
I am interested in the particle dark matter produced by the thermal freeze-out mechanism.

The thermally averaged annihilation cross section \(\langle\sigma v\rangle \) plays a crucial role to determine the relic abundance and the signal strength of indirect detection experiments.

Strong CP Problem

There are two parameters in the Standard Model which violate CP symmetry, the complex phase \(\delta_{\rm CP}\) of the CKM matrix and the QCD \(\bar \theta\) parameter. Although the value of \(\bar \theta\) is expected to be comparable to \(\delta_{\rm CP}\sim {\cal O}(1)\), there is an upper bound \(|\bar{\theta}|\lesssim 10^{-10}\) from neutron EDM measurements. This hierarchy problem is called the strong CP problem.
The QCD axion is one of the promising solution of the problem, and I study its phenomenology.