Hydrodynamic fluctuations and long-time tails in a fluid on an anisotropic background

TL;DR

This paper investigates how strong magnetic fields influence long-time correlation tails in relativistic fluids with conserved charges, revealing additional non-dissipative transport effects due to anisotropy.

Contribution

It extends hydrodynamic theory to include anisotropic effects of magnetic fields, identifying new transport parameters and computing their impact on long-time tails in correlation functions.

Findings

Magnetic fields increase the number of transport parameters from 3 to 10.

Identification of 3 non-dissipative transport parameters in anisotropic hydrodynamics.

Explicit calculation of long-time tails in stress tensor correlations under magnetic fields.

Abstract

The effective low-energy late-time description of many body systems near thermal equilibrium provided by classical hydrodynamics in terms of dissipative transport phenomena receives important corrections once the effects of stochastic fluctuations are taken into account. One such physical effect is the occurrence of long-time power law tails in correlation functions of conserved currents. In the hydrodynamic regime $\vec{k} \rightarrow 0$ this amounts to non-analytic dependence of the correlation functions on the frequency $\omega$. In this article, we consider a relativistic fluid with a conserved global $U(1)$ charge in the presence of a strong background magnetic field, and compute the long-time tails in correlation functions of the stress tensor. The presence of the magnetic field renders the system anisotropic. In the absence of the magnetic field, there are three out-of-equilibrium transport parameters that arise at the first order in the hydrodynamic derivative expansion, all of which are dissipative. In the presence of a background magnetic field, there are ten independent out-of-equilibrium transport parameters at the first order, three of which are non-dissipative and the rest are dissipative. We provide the most general linearized equations about a given state of thermal equilibrium involving the various transport parameters in the presence of a magnetic field, and use them to compute the long-time tails for the fluid.