Non-boost-invariant anisotropic dynamics

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)$(0+1)$-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.