Dissecting the string theory dual to QCD

Input from QCD and string theory is used in order to elucidate basic features of the string theory dual of QCD, It is argued that the relevant string theory is a five-dimensional version of the type-0 superstring. The vacuum solution is asymptotically AdS(5), and the geometry near the boundary is stringy. The structure of YM perturbation theory however emerges near the boundary. In the IR, the theory is argued to be well-approximated by a two-derivative truncation that takes into account strong coupling effects. This explains the success of previously proposed five-dimensional Eistein-dilaton gravity with an appropriate potential to describe salient features of the strong YM dynamics. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim