Ph.D., University of Tokyo, 2020
My research interests lie in Cosmology. So far, I have studied the early Universe in terms of primordial black holes (PBHs), gravitational waves (GWs), cosmic microwave background (CMB), and big bang nucleosynthesis (BBN). In my works on PBHs, I have shown that the double inflation model could produce the PBHs that can explain BHs detected by LIGO-Virgo collaboration or dark matter, being consistent with the current observational constraints. These works could be a bridge between the inflation era and the astrophysical observations of PBHs. In my works about GWs, I have focused on GWs induced by scalar perturbations. I have shown that the early matter dominated era, followed by the radiation dominated era, could enhance the induced GWs very much. The enhanced GWs could be probed by the future GW detectors. In addition to the above works, I have also discussed circular polarizations in CMB that are induced by the chiral GWs and constraints on the small-scale scalar perturbations from BBN.