Bulk and Shear Viscosity in Hagedorn Fluid

TL;DR

This paper derives expressions for bulk and shear viscosities in a Hagedorn fluid using relativistic kinetic theory, considering decay and van der Waals processes, with applications to heavy-ion collisions and cosmology.

Contribution

It introduces a new calculation of transport coefficients for Hagedorn fluids incorporating decay and van der Waals effects within relativistic kinetic theory.

Findings

Derived formulas for bulk and shear viscosities in Hagedorn fluid.

Analyzed in-medium thermal effects on viscosities and relaxation times.

Discussed implications for heavy-ion collision dynamics and cosmological models.

Abstract

Assuming that the Hagedorn fluid composed of known particles and resonances with masses $m<2\,$GeV obeys the {\it first-order} theory (Eckart) of relativistic fluid, we discuss the transport properties of QCD confined phase. Based on the relativistic kinetic theory formulated under the relaxation time approximation, expressions for bulk and shear viscosity in thermal medium are derived. The relaxation time in the Hagedorn dynamical fluid exclusively takes into account the decay and eventually van der Waals processes. We comment on the {\it in-medium} thermal effects on bulk and shear viscosities and averaged relaxation time with and without the excluded-volume approach. As an application of these results, we suggest the dynamics of heavy-ion collisions, non-equlibrium thermodynamics and the cosmological models, which require thermo and hydrodynamics equations of state.