We derive relativistic viscous hydrodynamic equations invoking the generalized second law of thermodynamics for two different forms of the nonequilibrium single-particle distribution function. We find that the relaxation times in these two derivations are identical for shear viscosity but different for bulk viscosity. These equations are used to study thermal dilepton and hadron spectra within longitudinal scaling expansion of the matter formed in relativistic heavy-ion collisions. For consistency, the same nonequilibrium distribution function is used in the particle production prescription as in the derivation of the viscous evolution equations. Appreciable differences are found in the particle production rates corresponding to the two nonequilibrium distribution functions. We emphasize that an inconsistent treatment of the nonequilibrium effects influences the particle production significantly, which may affect the extraction of transport properties of quark-gluon plasma.
R. S. Bhalerao, Jaiswal, A., Pal, S., and V. Sreekanth, “Particle production in relativistic heavy-ion collisions: A consistent hydrodynamic approach”, PHYSICAL REVIEW C, vol. 88, no. 4, p. 044911, 2013.