Dissipation in the very early stage of the hydrodynamic evolution in relativistic heavy ion collisions

TL;DR

This paper introduces a modified hydrodynamic model for ultrarelativistic nuclear collisions that accounts for initial pressure anisotropy and its relaxation, revealing significant effects on entropy and particle spectra.

Contribution

It presents a new approach to modeling early-stage dissipation in relativistic heavy ion collisions by modifying the energy-momentum tensor to include pressure anisotropy.

Findings

Relative entropy increases by about 30%.

Transverse momentum spectra are significantly hardened.

No effect observed on HBT radii.

Abstract

We propose a modification of the hydrodynamic model of the dynamics in ultrarelativistic nuclear collisions. A modification of the energy-momentum tensor at the initial stage describes the lack of isotropization of the pressure. Subsequently, the pressure is relaxing towards the equilibrium isotropic form in the local comoving frame. Within the Bjorken scaling solution a bound is found on the decay time of the initial anisotropy of the energy-momentum tensor. For the strongest dissipative effect allowed, we find a relative entropy increase of about 30%, a significant hardening of the transverse momentum spectra, and no effect on the HBT radii.