Shear viscosity of hadrons with K-matrix cross sections

TL;DR

This paper calculates the shear viscosity and entropy density of a hadronic resonance gas using unitarity-preserving K-matrix cross sections, revealing a significant reduction in /s near the QCD phase transition.

Contribution

It introduces a method to compute shear viscosity and entropy density using K-matrix parametrization, including a comprehensive resonance analysis up to 2 GeV.

Findings

Resonance interactions lower shear viscosity.

Resonance interactions increase entropy density.

/s decreases significantly near the QCD transition temperature.

Abstract

Shear viscosity \eta and entropy density s of a hadronic resonance gas are calculated using the Chapman-Enskog and virial expansion methods using the K-matrix parametrization of hadronic cross sections which preserves the unitarity of the T -matrix. In the \pi-K-N-\eta- mixture considered, a total of 57 resonances up to 2 GeV were included. Comparisons are also made to results with other hadronic cross sections such as the Breit-Wigner (BW) and, where available, experimental phase shift parametrizations. Hadronic interactions forming resonances are shown to decrease the shear viscosity and increase the entropy density leading to a substantial reduction of \eta/s as the QCD phase transition temperature is approached.