Transport Properties of QCD at Large $N_c$ and the Gauge/String Duality

Abstract

Below the deconfinement phase transition large $N_c$ QCD is expected to be a very viscous hadronic fluid because both the shear and bulk viscosity to entropy density ratio, $\eta /s,\zeta /s\sim N_c^2$. In this letter I show that $\eta /s\sim N_c^2$ in the confined phase of holographic models of QCD at large $N_c$ defined in the supergravity approximation. Our results show that the gauge/string duality can be used to describe not only nearly perfect fluids but also extremely viscous systems such as a cold gas of glueballs.

arXiv comment10 pages, conclusions changed, references added

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