Reheating formulas in Quintessential Inflation via Gravitational Particle Production

We calculate the reheating temperature in scenarios where heavy particles are gravitationally produced during a phase transition. We explore two distinct situations: the decay of these particles both during and after the kination phase. Subsequently, we determine the respective reheating temperatures. Finally, we constrain these temperatures based on considerations related to the overproduction of Gravitational Waves during the phase transition from the end of inflation to the onset of kination.