Phenomenological bound on the viscosity of the hadron resonance gas

TL;DR

This paper investigates bounds on the shear viscosity to entropy density ratio in hadronic matter using a phenomenological approach within an ideal hadron resonance gas model, providing bounds that are close to quantum limits.

Contribution

It introduces a phenomenological restriction to estimate upper and lower bounds of transport coefficients in hadronic matter, refining previous estimations.

Findings

Lower bound for shear viscosity to entropy density ratio is slightly above quantum lower bound.

The phenomenological restriction helps to narrow down transport coefficient estimations.

Bounds can be tuned within a proposed numerical band using the restriction.

Abstract

We have explored some phenomenological issues during calculations of transport coefficients for hadronic matter, produced in the experiments of heavy ion collisions. Here, we have used an ideal hadron resonance gas model to demonstrate the issues. On the basis of dissipation mechanism, the hadronic zoo is classified into resonance and non-resonance members, who participate in dissipation via strong decay and scattering channels respectively. Imposing our phenomenological restriction, we are able to provide a rough upper and lower bound estimations of transport coefficients. Interestingly, we find that our proposed lower limit estimation for shear viscosity to entropy density ratio is little larger than its quantum lower bound. By taking a simple example, we have demonstrated how our proposed restriction help to tune any estimation of transport coefficients within its numerical band, proposed by us.