2PI simulations in expanding backgrounds: Doing it anyway!

TL;DR

This paper develops a 2PI formalism for quantum fields in expanding universes, enabling self-consistent evolution of quantum fields and cosmology, with sample calculations showing equilibration processes.

Contribution

It introduces a 2PI approach to quantum fields in Friedmann-Robertson-Walker backgrounds, including a renormalised semi-classical Friedmann equation and sample equilibration calculations.

Findings

Demonstrates kinetic and chemical equilibration in expanding backgrounds

Provides a self-consistent method for quantum field and cosmological evolution

Shows the feasibility of 2PI formalism in cosmological settings

Abstract

I set out the 2PI formalism for quantum fields in a Friedmann-Robertson-Walker Universe. I show how one can solve self-consistently for the quantum field evolution and the evolution of the cosmological scale factor, using a renormalised semi-classical Friedmann equation. In a 2PI coupling expansion truncated at O(lambda^2), I perform sample calculations demonstrating kinetic and chemical equilibration in this context.