Building a "holographic dual" to QCD in the AdS$_5$: instantons and confinement

Abstract

Recent attempts to find a ``holographic dual'' to QCD-like theories included a suggestion by Karsh et al (below referred to as KKSS) to incorporate confinement via a potential quadratically increasing into the 5-th direction of the $AdS_5$ space. We show that the same conclusion follows from completely different line of arguments. If instantons are promoted into the 5d space by identifying the instanton size $\rho$ at the 5-th coordinate, the background geometry necessarily should be the AdS$_5$. As I argued already in 1999, confinement described via ``dual superconductivity'' leads to a factor $exp(-2\pi\sigma\rho^2)$, where $\sigma$ is a string tension, which is nearly exactly identical to that suggested by KKSS. This expression is also well supported by available lattice data. At the end of the paper we propose a IR potential generalized to the nonzero temperatures.