Reheating after quintessential inflation and gravitational waves

We investigate the dependence of the gravitational wave spectrum from quintessential inflation on the reheating process. We consider two extreme reheating processes. One is the gravitational reheating by particle creation in the expanding universe in which the beginning of the radiation-dominated epoch is delayed because of the domination of the kinetic energy of inflaton (kination). The other is the instant preheating considered by Felder et al in which the universe becomes radiation dominated soon after the end of inflation. We find that the spectrum of gravitational waves at similar to 100 MHz is quite sensitive to the reheating process. This result is not limited to quintessential inflation but applicable to various inflation models. Conversely, the detection or non-detection of primordial gravitational waves at similar to 100 MHz would provide useful information regarding the reheating process in inflation.