Backreaction Effects on Nonequilibrium Spectral Function

TL;DR

This paper investigates how including back-reaction effects alters the spectral function of a scalar theory, revealing damping phenomena that impact particle behavior in early universe conditions.

Contribution

It introduces a method to compute spectral functions with back-reaction effects using the Kadanoff-Baym equation and Keldysh formalism, highlighting the differences from the equilibrium case.

Findings

Neglecting back-reaction yields an equilibrium Breit-Wigner spectral function.

Including back-reaction causes damping in the spectral function.

Damping modifies particle damping rates in a thermal bath, with implications for early universe physics.

Abstract

We show how to compute the spectral function for a scalar theory in two different scenarios: one which disregards back-reaction i.e. the response of the environment to the external particle, and the other one where back-reaction is considered. The calculation was performed using the Kadanoff-Baym equation through the Keldysh formalism. When back-reaction is neglected, the spectral function is equal to the equilibrium one, which can be represented as a Breit-Wigner distribution. When back-reaction is introduced we observed a damping in the spectral function of the thermal bath. Such behavior modifies the damping rate for particles created within the bath. This certainly implies phenomenological consequences right after the Big-Bang, when the primordial bath was created.