Nonlinear causality of general first-order relativistic viscous hydrodynamics

Understand

Effective theory arguments are used to derive the most general energy-momentum tensor of a relativistic viscous fluid with an arbitrary equation of state (in the absence of other conserved currents) that is first-order in the derivatives of the energy density and flow velocity and does not include extended variables such as in Mueller-Israel-Stewart-like theories.

• This energy-momentum tensor leads to a causal theory, provided one abandons the usual conventions for the out-of-equilibrium hydrodynamic variables put forward by Landau-Lifshitz and Eckart.
• In particular, causality requires nonzero out-of-equilibrium energy density corrections and heat flow.
• Conditions are found to ensure linear stability around equilibrium in flat space-time.