Non-boost-invariant anisotropic dynamics

TL;DR

This paper develops a framework for modeling the non-boost-invariant evolution of a quark-gluon plasma with large momentum-space anisotropies, extending traditional hydrodynamics to include anisotropic states and their dynamics.

Contribution

It introduces an anisotropic expansion approach around a non-equilibrium state, deriving coupled PDEs for anisotropy, momentum scale, and flow, capturing deviations from Bjorken scaling.

Findings

Quantitative analysis of pressure anisotropy evolution.

Comparison of strong and weak coupling limits.

Extension of hydrodynamics to anisotropic, non-boost-invariant regimes.

Abstract

We study the non-boost-invariant evolution of a quark-gluon plasma subject to large early-time momentum-space anisotropies. Rather than using the canonical hydrodynamical expansion of the distribution function around an isotropic equilibrium state, we expand around a state which is anisotropic in momentum space and parameterize this state in terms of three proper-time and spatial-rapidity dependent parameters. Deviations from the Bjorken scaling solutions are naturally taken into account by the time evolution of the spatial-rapidity dependence of the anisotropic ansatz. As a result, we obtain three coupled partial differential equations for the momentum-space anisotropy, the typical momentum of the degrees of freedom, and the longitudinal flow. Within this framework (0+1)-dimensional Bjorken expansion is obtained as an asymptotic limit. Finally, we make quantitative comparisons of the temporal and spatial-rapidity evolution of the dynamical parameters and resulting pressure anisotropy in both the strong and weak coupling limits.