Generalized relativistic hydrodynamics with a convex extension
  We propose a new model which describes relativistic hydrodynamics and generalizes the standard Euler system of isentropic perfect fluids. Remarkably, our system admits a convex extension which allows us to transform it to a symmetric hyperbolic form. This result sheds new light even on the relativistic Euler system. 
Robert Beig and Philippe G. LeFloch
gr-qc