Holography and unquenched quark-gluon plasmas

We employ the string/gauge theory correspondence to study properties of strongly coupled quark-gluon plasmas in thermal gauge theories with a large number of colors and flavors. In particular, we analyze noncritical string duals of conformal (S)QCD, as well as ten-dimensional wrapped fivebrane duals of SQCD-like theories. We study general properties of the dual plasmas, including the drag force exerted on a probe quark and the jet quenching parameter. We find that these plasma observables depend on the number of colors and flavors in the 'QCD dual'; in particular, we find that the jet quenching parameter increases linearly with N{sub f}/N{sub c} at leading order in the probe limit. In the ten-dimensional case we find a nontrivial drag coefficient but a vanishing jet quenching parameter. We comment on the relation of this result with total screening and argue that the same features are shared by all known plasmas dual to fivebranes in ten dimensions. We also construct new D5 black hole solutions with spherical horizon and show that they exhibit the same features.