Thermal effects and scalar modes in the cosmological propagation of gravitational waves

TL;DR

This paper investigates how thermal effects influence the propagation of gravitational waves in cosmological settings, especially near singularities, considering both standard and modified gravity theories and their impact on scalar and tensor modes.

Contribution

It introduces an analysis of thermal radiation effects on gravitational wave dynamics in scalar field cosmologies, including in modified gravity frameworks like $F(R)$ gravity.

Findings

Thermal radiation can significantly alter gravitational wave behavior near cosmological singularities.

Thermal effects can cause both enhancement and dissipation of gravitational wave amplitudes.

The study discusses potential methods to detect and distinguish scalar and tensor gravitational modes in the stochastic background.

Abstract

We consider thermal effects in the propagation of gravitational waves on a cosmological background. In particular, we consider scalar field cosmologies and study gravitational modes near cosmological singularities. We point out that the contribution of thermal radiation can heavily affect the dynamics of gravitational waves giving enhancement or dissipation effects both at quantum and classical level.These effects are considered both in General Relativity and in modified theories like $F(R)$ gravity which can be easily reduced to scalar-tensor cosmology. The possible detection and disentanglement of standard and scalar gravitational modes on the stochastic background are also discussed.