Bound for entropy and viscosity ratio for strange quark matter

Abstract

High energy density ($\eps$) and temperature (T) links general relativity and hydrodynamics leading to a lower bound for the ratio of shear viscosity ($\hat{I}\cdot$) 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 $T\sim 80MeV$. 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 $\hat{I}\cdot /s$ 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 $T=80MeV$ seem to constitute the most perfect interacting fluid permitted by nature.

10 pages, 2 figures, 1 table; Accepted for publication in Phys. Lett. B