Particle production in relativistic heavy-ion collisions: A consistent hydrodynamic approach

We derive relativistic viscous hydrodynamic equations using the
generalized second law of thermodynamics for two different forms of
the non-equilibrium single-particle distribution function. 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 non-equilibrium
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 non-equilibrium distribution functions. We show that an
inconsistent treatment of the non-equilibrium effects influences the
particle production significantly, which may affect the extraction of
transport properties of quark-gluon plasma. We also show that
correction to the distribution function obtained using alternative
Chapman-Enskog method ensures observed m_T^(-1/2) scaling of the
longitudinal HBT radii, unlike the popular Grad's method
expression. We also demonstrate the rapid convergence of this
alternative method expansion up to second order.