Anisotropic hydrodynamics for conformal Gubser flow

TL;DR

This paper develops anisotropic hydrodynamics equations for Gubser flow, demonstrating improved accuracy over existing methods and exact solutions in certain limits, by assuming ellipsoidal momentum distributions and exploiting symmetries.

Contribution

It derives and numerically solves anisotropic hydrodynamics equations tailored for Gubser flow, showing superior performance and exactness in specific regimes compared to prior approaches.

Findings

Anisotropic hydrodynamics better describes system evolution than existing approaches.

The derived equations are exact in ideal and free-streaming limits.

Numerical solutions match exact Boltzmann equation results in tested regimes.

Abstract

We derive the equations of motion for a system undergoing boost-invariant longitudinal and azimuthally-symmetric transverse "Gubser flow" using leading-order anisotropic hydrodynamics. This is accomplished by assuming that the one-particle distribution function is ellipsoidally-symmetric in the momenta conjugate to the de Sitter coordinates used to parameterize the Gubser flow. We then demonstrate that the SO(3)_q symmetry in de Sitter space further constrains the anisotropy tensor to be of spheroidal form. The resulting system of two coupled ordinary differential equations for the de Sitter-space momentum scale and anisotropy parameter are solved numerically and compared to a recently obtained exact solution of the relaxation-time-approximation Boltzmann equation subject to the same flow. We show that anisotropic hydrodynamics describes the spatio-temporal evolution of the system better than all currently known dissipative hydrodynamics approaches. In addition, we prove that anisotropic hydrodynamics gives the exact solution of the relaxation-time approximation Boltzmann equation in the ideal, eta/s -> 0, and free-streaming, eta/s -> infinity, limits.