Nonlinear Constraints on Relativistic Fluids Far from Equilibrium

New constraints are found that must necessarily hold for Israel-Stewart-like theories of fluid dynamics to be causal far away from equilibrium. Conditions sufficient ensure causality, local existence, and uniqueness solutions in these also presented. Our results the full nonlinear regime, taking into account bulk shear viscosities (at zero chemical potential), without any simplifying symmetry or near-equilibrium assumptions. findings provide fundamental on magnitude viscous corrections