The dynamics of cosmological perturbations in thermal $\lambda\phi^4$ theory

TL;DR

This paper extends a thermal-field-theory approach to cosmological perturbations by including weak self-interactions in a scalar field model, providing explicit solutions for various modes in a radiation-dominated universe.

Contribution

It generalizes previous collisionless solutions to include weak self-interactions up to order rac{}{2}, incorporating thermal mass resummation and nonlocal gravitational effects.

Findings

Explicit solutions for scalar, vector, and tensor modes

Inclusion of thermal mass effects and nonlocal vertices

Application to radiation-dominated cosmological models

Abstract

Using a recent thermal-field-theory approach to cosmological perturbations, the exact solutions that were found for collisionless ultrarelativistic matter are generalized to include the effects from weak self-interactions in a $\lambda\phi^4$ model through order $\lambda^{3/2}$. This includes the effects of a resummation of thermal masses and associated nonlocal gravitational vertices, thus going far beyond classical kinetic theory. Explicit solutions for all the scalar, vector, and tensor modes are obtained for a radiation-dominated Einstein-de Sitter model containing a weakly interacting scalar plasma with or without the admixture of an independent component of perfect radiation fluid.