Transport Coefficients of Hadronic Matter near $T_c$

TL;DR

This paper uses a hadron resonance gas model to estimate the shear viscosity to entropy density ratio of hadronic matter near the critical temperature, finding values close to the conjectured lower bound and aligning with lattice QCD results.

Contribution

It introduces a comprehensive hadron resonance gas model including Hagedorn states to bound the shear viscosity near $T_c$, providing insights into transport properties of hadronic matter.

Findings

Estimated $ ext{eta}/s$ near $T_c$ is approximately $1/(4 extpi)$.

Found a large trace anomaly and small speed of sound near $T_c$.

Results agree with recent lattice QCD calculations.

Abstract

A hadron resonance gas model including all known particles and resonances with masses $m<2$ GeV and an exponentially rising density of Hagedorn states for $m>2$ GeV is used to obtain an upper bound on the shear viscosity to entropy density ratio, $\eta/s\approx1/(4\pi)$, of hadronic matter near $T_c$. We found a large trace anomaly and small speed of sound near $T_c$, which agree well with recent lattice calculations. We comment on the bulk viscosity to entropy density ratio close to $T_c$.