Shear viscosity to entropy density ratio of a relativistic Hagedorn resonance gas

TL;DR

This paper calculates the shear viscosity to entropy density ratio of a relativistic Hagedorn resonance gas, showing it decreases with temperature and approaches values similar to a strongly coupled quark-gluon plasma near the deconfinement transition.

Contribution

It provides a theoretical estimate of eta/s for a Hagedorn resonance gas, linking it to the properties of quark-gluon plasma near the critical temperature.

Findings

eta/s decreases with increasing temperature

minimum eta/s near critical temperature matches quark-gluon plasma estimates

resonance multiplicity growth influences viscosity behavior

Abstract

The new state of matter produced at Relativistic Heavy Ion Collider reveals a strongly coupled quark-gluon plasma with an extremely small shear viscosity to entropy density ratio eta/s. We calculate the eta/s of an equilibrated hadron matter characterized by a relativistic hadron resonance gas with a Hagedorn mass spectrum that grows exponentially with the hadron mass. We find with increase in temperature of the system the eta/s value decreases due to rapid increase in the multiplicity of massive resonances. In the vicinity of the critical temperature for deconfinement transition, the minimum value of eta/s in the Hagedorn resonance gas is found to be consistent with the current estimates for a strongly coupled quark-gluon plasma.