Second order hydrodynamic coefficients from kinetic theory

TL;DR

This paper calculates second-order hydrodynamic coefficients in weakly coupled QCD, QED, and scalar phi^4 theory using kinetic theory, addressing the need for stable and causal relativistic hydrodynamics.

Contribution

It provides the first perturbative computation of second-order hydrodynamic coefficients in QCD, extending previous work limited to supersymmetric theories at infinite coupling.

Findings

Second-order coefficients computed for QCD, QED, and scalar theories.

Results obtained perturbatively to leading order in coupling.

Addresses stability and causality issues in relativistic hydrodynamics.

Abstract

In a relativistic setting, hydrodynamic calculations which include shear viscosity (which is first order in an expansion in gradients of the flow velocity) are unstable and acausal unless they also include terms to second order in gradients. To date such terms have only been computed in supersymmetric N=4 Super-Yang-Mills theory at infinite coupling. Here we compute these second-order hydrodynamic coefficients in weakly coupled QCD, perturbatively to leading order in the QCD coupling, using kinetic theory. We also compute them in QED and scalar lambda phi^4 theory.