Renormalization out of equilibrium in a superrenormalizable theory

TL;DR

This paper develops a renormalization scheme for nonequilibrium quantum field theory that handles initial conditions far from equilibrium, avoiding divergences through non-Gaussian initial states and applicable to thermalization studies.

Contribution

It introduces a renormalization approach for the initial value problem in nonequilibrium QFT using Kadanoff-Baym equations and non-Gaussian initial states, addressing time-dependent divergences.

Findings

Renormalized time evolution of two-point functions achieved.

Cutoff-dependent effects and initial-time singularities are avoided.

Scheme applicable to systems far from equilibrium and thermalization processes.

Abstract

We discuss the renormalization of the initial value problem in Nonequilibrium Quantum Field Theory within a simple, yet instructive, example and show how to obtain a renormalized time evolution for the two-point functions of a scalar field and its conjugate momentum at all times. The scheme we propose is applicable to systems that are initially far from equilibrium and compatible with non-secular approximation schemes which capture thermalization. It is based on Kadanoff-Baym equations for non-Gaussian initial states, complemented by usual vacuum counterterms. We explicitly demonstrate how various cutoff-dependent effects peculiar to nonequilibrium systems, including time-dependent divergences or initial-time singularities, are avoided by taking an initial non-Gaussian three-point vacuum correlation into account.