Adiabatic hydrodynamics: The eightfold way to dissipation

Understand

We provide a complete solution to hydrodynamic transport at all orders in the gradient expansion compatible with the second law constraint.

• The key new ingredient we introduce is the notion of adiabaticity, which allows us to take hydrodynamics off-shell.
• Adiabatic fluids are such that off-shell dynamics of the fluid compensates for entropy production.
• The space of adiabatic fluids is quite rich, and admits a decomposition into seven distinct classes.