Remarks concerning bulk viscosity of hadron matter in relaxation time   ansatz
  The bulk viscosity is calculated for hadron matter produced in heavy-ion collisions, being described in the relaxation time approximation withi n the relativistic mean- field-based model with scaled hadron masses and couplings. W e show how different approximations used in the literature affect the result. Nume rical evaluations of the bulk viscosity with three considered models deviate not much from each other confirming earlier results. 
A. S. Khvorostukhin, V. D. Toneev, D. N. Voskresensky
nucl-th hep-ph