Chemical Equilibration and Transport Properties of Hadronic Matter near $T_c$

TL;DR

This paper demonstrates that including Hagedorn states near the critical temperature explains rapid chemical equilibration and matches experimental hadron ratios at RHIC, while also aligning with lattice and string theory viscosity bounds.

Contribution

It introduces a resonance gas model with Hagedorn states that accurately predicts chemical equilibration times, hadron ratios, and transport properties near $T_c$, connecting experimental, lattice, and theoretical results.

Findings

Hagedorn states enable rapid chemical equilibration near $T_c$

Model reproduces RHIC hadron ratios accurately

Estimated $ ext{eta}/s$ near $T_c$ approaches the string theory bound

Abstract

We discuss how the inclusion of Hagedorn states near $T_c$ leads to short chemical equilibration times of proton anti-proton pairs, $K\bar{K}$ pairs, and $\Lambda\bar{\Lambda}$ pairs, which indicates that hadrons do not need to be "born" into chemical equilibrium in ultrarelativistic heavy ion collisions. We show that the hadron ratios computed within our model match the experimental results at RHIC very well. Furthermore, estimates for $\eta/s$ near $T_c$ computed within our resonance gas model are comparable to the string theory viscosity bound $\eta/s=1/4\pi$. Our model provides a good description of the recent lattice results for the trace anomaly close to $T_c=196$ MeV.