New formulation of leading order anisotropic hydrodynamics

TL;DR

This paper introduces a new formulation of anisotropic hydrodynamics for (1+1)-dimensional flow, improving agreement with Boltzmann solutions, especially for finite mass particles, and aligning with Israel-Stewart theory near equilibrium.

Contribution

The paper presents a novel formulation of leading order anisotropic hydrodynamics for (1+1)-dimensional flow, enhancing accuracy and consistency with established theories.

Findings

Better agreement with Boltzmann solutions for finite mass particles

Consistent with Israel-Stewart near equilibrium

Improved modeling of ultrarelativistic heavy-ion collisions

Abstract

Anisotropic hydrodynamics is a reorganization of the relativistic hydrodynamics expansion, with the leading order already containing substantial momentum-space anisotropies. The latter are a cause of concern in the traditional viscous hydrodynamics, since large momentum anisotropies generated in ultrarelativistic heavy-ion collisions are not consistent with the hypothesis of small deviations from an isotropic background, i.e., from the local equilibrium distribution. We discuss the leading order of the expansion, presenting a new formulation for the (1+1)--dimensional case, namely, for the longitudinally boost invariant and cylindrically symmetric flow. This new approach is consistent with the well established framework of Israel and Stewart in the close to equilibrium limit (where we expect viscous hydrodynamics to work well). If we consider the (0+1)--dimensional case, that is, transversally homogeneous and longitudinally boost invariant flow, {the new form of anisotropic hydrodynamics leads to better agreement with known solutions} of the Boltzmann equation than the previous formulations, especially when we consider finite mass particles.