Abstract : The Higgs inflation perfectly agrees with the CMB observation, but suffers from a unitarity problem due to a large non-minimal coupling of Higgs field to the Ricci scalar. Recently, it has been shown that introducing a Ricci square term (R2 term) in the Higgs inflation can solve this problem.
In this talk, we discuss the post-inflationary dynamics for reheating and freeze-in dark matter in the Higgs-R2 model. Taking the perturbative approach for reheating, we determine the evolution of the temperature for radiation bath produced during inflation and determine the maximum and reheating temperatures of the Universe. Also, adopting a singlet scalar dark matter, we discuss the freeze-in production of dark matter both from the non-thermal scattering during reheating and the thermal scattering after reheating.