Bound for entropy and viscosity ratio for strange quark matter

TL;DR

This paper derives a lower bound for the ratio of shear viscosity to entropy density in strange quark matter, showing it is saturated at the star's surface at around 80 MeV, indicating a nearly perfect fluid.

Contribution

It presents a model linking general relativity and hydrodynamics to establish a bound on viscosity and entropy ratio in strange quark matter, with implications for the nature of quark-gluon plasma.

Findings

Bound for η/s is saturated at the star's surface at T ~ 80 MeV.

Inside the star, η/s increases with density, consistent with perturbative QCD results.

Deconfined quarks at the surface form the most perfect fluid allowed by nature.

Abstract

High energy density ($\eps$) and temperature (T) links general relativity and hydrodynamics leading to a lower bound for the ratio of shear viscosity ($\eta$) and entropy density ($s$). We get the interesting result that the bound is saturated in the simple model for quark matter that we use for strange stars at the surface for $T \sim 80 MeV$. At this $T$ we have the possibility of cosmic separation of phases. At the surface of the star where the pressure is zero - the density $\eps$ has a fixed value for all stars of various masses with correspondingly varying central energy density $\eps_c$. Inside the star where this density is higher, the ratio of $\eta/s$ is larger and are like the known results found for perturbative QCD. This serves as a check of our calculation. The deconfined quarks at the surface of the strange star at $T = 80 MeV$ seem to constitute the most perfect interacting fluid permitted by nature.