My interests lie in the strong connection between particle physics and cosmology in the early universe. In particular, I have been focusing on its dynamical aspects from the viewpoint of quantum fields under extreme conditions. This is partly because the early universe was filled with very hot plasma as strongly suggested by the observations of CMB and the success of BBN. I try to refine understanding of various phenomena in the early universe, like preheating/reheating, baryo/leptogenesis, dark matter production, and cosmological phase transition, which are closely tied with new physics.