Gravitational Wave from Graviton Bremsstrahlung during Reheating

TL;DR

This paper investigates graviton production during reheating after inflation, revises decay rate calculations, and explores the potential for detecting the resulting high-frequency gravitational wave background with future detectors.

Contribution

It provides corrected decay rate calculations and predicts a high-frequency stochastic GW background from reheating, linking cosmological processes to potential experimental detection.

Findings

Revised 3-body decay rates differ from previous literature.

Calculated the stochastic GW background during reheating.

Projected detectability with microwave cavities and space-based detectors.

Abstract

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 $\Delta N_\text{eff}$, 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.