Gravitational wave from graviton Bremsstrahlung during reheating

We revisit graviton production via Bremsstrahlung from the decay of the inflaton during inflationary reheating. Using two complementary computational techniques, we first show that such 3-body differential decay rates differ from previously reported results in the literature. We then compute the stochastic gravitational wave (GW) background that forms during the period of reheating, when the inflaton perturbatively decays with the radiative emission of gravitons. By computing the number of relativistic degrees of freedom in terms of ANeff, we constrain the resulting GW energy density from BBN and CMB. Finally, we project current and future GW detector sensitivities in probing such a stochastic GW background, which typically peaks in the GHz to THz ballpark, opening up the opportunity to be detected with microwave cavities and space-based GW detectors.

Automated summary

In this study, we investigate graviton production during inflationary reheating through the process of Bremsstrahlung from the decay of the inflaton. We demonstrate that the differential decay rates for the 3-body process differ from previously reported results. Additionally, we calculate the stochastic gravitational wave (GW) background formed during reheating and explore the prospects of detecting it using current and future GW detectors.