Gravitational waves from second-order scalar perturbations

by Dr Sachiko Kuroyanagi (Nagoya Univ.)

Monday 11 Apr 2016, 15:00 → 16:00 Asia/Seoul

Inflation is now widely considered to be the most attractive scenario for describing the early evolution of the Universe. One of the reasons why inflation succeeds as a standard paradigm is that it not only solves problems in the big bang theory but also predicts an almost scale-invariant spectrum of scalar (density) perturbations originating from quantum fluctuations.  It has been suggested that the scalar perturbations generate gravitational waves at second order.  Previous works have shown that gravitational waves are generated efficiently in matter-dominated era due to the growth of density perturbations on sub-Hubble scales.  If the Universe have experienced reheating with inflaton oscillations where the Universe behaves like matter-dominated era, large enhancement of gravitational waves is possible in the frequency range of direct detection experiments.  We numerically solve the evolution of gravitational waves from second-order scalar perturbations and investigate the effect of the potential decays due to the sound speed at the end of the early matter era.  We also discuss about the detectability of the gravitational waves by future experiments.