Shear viscosity of a relativistic scalar field from functional renormalization

TL;DR

This paper derives renormalization group flow equations for the shear viscosity of a relativistic scalar field, providing a systematic non-perturbative approach to compute transport coefficients.

Contribution

It introduces a minimal truncation scheme within the flow equation method to reliably calculate shear viscosity in a relativistic scalar field theory.

Findings

Flow equations include branch cut contributions to self energy and vertex.

The method extends perturbative resummation schemes systematically.

A reliable shear viscosity coefficient is obtained from the minimal truncation.

Abstract

Renormalization group flow equations of the fluid dynamical shear viscosity transport coefficient of a relativistic real scalar field are derived. The flowing effective action contains branch cut contributions to the self energy and interaction vertex in the symmetric phase. We demonstrate how the flow equation method can systematically extend the perturbative resummation schemes. We show that our truncation is in that sense a minimal scheme in which a reliable viscosity coefficient is obtained.