Anisotropic hydrodynamics with a scalar collisional kernel

TL;DR

This study explores how using a more realistic scalar collisional kernel affects the non-equilibrium dynamics in anisotropic hydrodynamics, revealing increased momentum-space anisotropy especially with Bose enhancement.

Contribution

It is the first to analyze the impact of a scalar 2<->2 scattering kernel on anisotropic hydrodynamics, comparing classical and quantum statistics.

Findings

Scalar kernel leads to higher momentum-space anisotropy.

Bose enhancement further increases anisotropy.

Anisotropic non-equilibrium attractor identified.

Abstract

Prior studies of non-equilibrium dynamics using anisotropic hydrodynamics have used the relativistic Anderson-Witting scattering kernel or some variant thereof. In this paper, we make the first study of the impact of using a more realistic scattering kernel. For this purpose, we consider a conformal system undergoing transversally-homogenous and boost-invariant Bjorken expansion and take the collisional kernel to be given by the leading order 2 <-> 2 scattering kernel in scalar lambda phi^4. We consider both classical and quantum statistics in order to assess the impact of Bose enhancement on the dynamics. We also determine the anisotropic non-equilibrium attractor of a system subject to this collisional kernel. We find that, when the near-equilibrium relaxation-times in the Anderson-Witting and scalar collisional kernels are matched, the scalar kernel results in a higher degree of momentum-space anisotropy during the system's evolution, given the same initial conditions. Additionally, we find that taking into account Bose enhancement further increases the dynamically generated momentum-space anisotropy.