Thermal Gravitational Waves During Reheating

TL;DR

This paper investigates how the reheating phase after inflation influences the generation and characteristics of stochastic gravitational waves from thermal plasma interactions, revealing enhanced amplitudes and shifted spectra.

Contribution

It extends previous models by including reheating effects, showing significant impacts on GW amplitude, spectrum shape, and contribution to effective neutrino species.

Findings

GW amplitude can be significantly enhanced during reheating

Peak frequency of GW spectrum shifts due to reheating dynamics

Reheating increases the contribution to $_N_ ext{eff}$

Abstract

In this work, we revisit the generation of stochastic gravitational waves (GWs) from interactions in the thermal plasma. We extend the existing literature by incorporating the reheating phase into the thermal history. Our results show that the amplitude of the GW spectrum can be significantly enhanced because the temperature during reheating can be much higher than the reheating temperature. Furthermore, since the temperature evolution during reheating differs from that of free radiation, the peak frequency of the spectrum can also shift. Additionally, the morphology of the spectrum can present characteristic features. We also compute the contribution of the integrated GW spectrum to the effective number of neutrino species, $\Delta N_\text{eff}$, which can be substantially larger.