Early dissipation and viscosity

TL;DR

This paper investigates how dissipative effects, including viscosity, influence the evolution and entropy production in relativistic heavy-ion collision fireballs, affecting flow dynamics and cooling rates.

Contribution

It provides a detailed analysis of dissipation and viscosity effects on the expansion dynamics of relativistic heavy-ion collision fireballs, including entropy and flow modifications.

Findings

Viscous effects increase entropy during expansion.

Viscosity reduces longitudinal cooling rate.

Transverse flow is enhanced by dissipation.

Abstract

We consider dissipative phenomena due to the relaxation of an initial anisotropic local pressure in the fireball created in relativistic heavy-ion collisions, both for the Bjorken boost-invariant case and for the azimuthally symmetric radial expansion with boost-invariance. The resulting increase of the entropy can be counterbalanced by a suitable retuning of the initial temperature. An increase of the transverse collective flow is observed. The influence of the shear viscosity on the longitudinal expansion is also studied. Viscosity reduces the cooling rate from the longitudinal work and counteracts the pressure gradients that accelerate the longitudinal flow.