General SIGW source for reheating dynamics

TL;DR

This paper derives a gauge-invariant source term for scalar-induced gravitational waves during reheating, accommodating a smooth transition from inflaton to radiation, enhancing understanding of early universe gravitational wave production.

Contribution

It provides a general, gauge-invariant derivation of the SIGW source term applicable during various reheating scenarios, including matter-dominated phases.

Findings

Derived the source term in an arbitrary gauge during reheating

Verified gauge invariance up to second order

Applicable to scenarios with smooth transition from inflaton to radiation

Abstract

Working in an arbitrary gauge, we derive the source term for scalar-induced gravitational waves (SIGW) valid during a general reheating epoch. Specifically, the dominant energy component is allowed to transition smoothly from an inflaton field to a radiation fluid, possibly via a period of matter domination. Gauge invariance is verified up to second order.