Holographic Viscosity of Fundamental Matter
Abstract
A holographic dual of a finite-temperature SU(Nc) gauge theory with a small number of flavours Nf << Nc typically contains D-branes in a black hole background. By considering the backreaction of the branes, we demonstrate that, to leading order in Nf/Nc, the viscosity to entropy ratio in these theories saturates the conjectured universal bound eta/s >= 1/4π. The contribution of the fundamental matter etafund is therefore enhanced at strong 't Hooft coupling lambda; for example, etafund ~ lambda Nc Nf T3 in four dimensions. Other transport coefficients are analogously enhanced. These results hold with or without a baryon number chemical potential.
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