Nonlinear Constraints on Relativistic Fluids Far From Equilibrium

Understand

New constraints are found that must necessarily hold for Israel-Stewart-like theories of fluid dynamics to be causal far away from equilibrium.

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