Nonconformal viscous anisotropic hydrodynamics

TL;DR

This paper extends viscous anisotropic hydrodynamics to include particle masses, deriving new equations and demonstrating improved accuracy over existing models in describing boost-invariant expansion.

Contribution

It introduces a generalized macroscopic theory for viscous anisotropic hydrodynamics with non-zero particle masses, incorporating bulk viscous effects at leading order.

Findings

Accurately approximates the exact Boltzmann solution in (0+1)-D expansion.

Outperforms existing hydrodynamic models in nonconformal scenarios.

Provides a new framework for systems with bulk viscous effects.

Abstract

We generalize the derivation of viscous anisotropic hydrodynamics from kinetic theory to allow for non-zero particle masses. The macroscopic theory is obtained by taking moments of the Boltzmann equation after expanding the distribution function around a spheroidally deformed local momentum distribution whose form has been generalized by the addition of a scalar field that accounts non-perturbatively (i.e. already at leading order) for bulk viscous effects. Hydrodynamic equations for the parameters of the leading-order distribution function and for the residual (next-to-leading order) dissipative flows are obtained from the three lowest moments of the Boltzmann equation. The approach is tested for a system undergoing (0+1)-dimensional boost-invariant expansion for which the exact solution of the Boltzmann equation in relaxation time approximation is known. Nonconformal viscous anisotropic hydrodynamics is shown to approximate this exact solution more accurately than any other known hydrodynamic approximation.