Anisotropic Hydrodynamics for Rapidly Expanding Systems

TL;DR

This paper provides an exact solution to the Boltzmann equation for a rapidly expanding system and demonstrates that anisotropic hydrodynamics offers a more accurate approximation than traditional viscous hydrodynamics.

Contribution

It introduces an exact solution for a specific expanding system and compares it with approximate hydrodynamic models, showing anisotropic hydrodynamics' superior accuracy.

Findings

Anisotropic hydrodynamics closely matches the exact solution.

Traditional viscous hydrodynamics is less accurate.

The study validates anisotropic hydrodynamics for expanding systems.

Abstract

We exactly solve the relaxation-time approximation Boltzmann equation for a system which is transversely homogeneous and undergoing boost-invariant longitudinal expansion. We compare the resulting exact numerical solution with approximate solutions available in the anisotropic hydrodynamics and second order viscous hydrodynamics frameworks. In all cases studied, we find that the anisotropic hydrodynamics framework is a better approximation to the exact solution than traditional viscous hydrodynamical approaches.