Small viscosity method and criteria for shock wave existence in   relativistic magnetic hydrodynamics
  We obtain criteria for shock wave (SW)existence in relativistic magnetic hydrodynamics with no suppositions about convexity of the equation of state. Method of derivation involves consideration of a continuous SW profile in presence of Landau-Lifshitz relativistic viscosity tensor with both non-zero viscosity coefficients. 
V.I.Zhdanov, M.S.Borshch