Linear confinement and AdS/QCD

In a theory with linear confinement, such as QCD, the masses squared m_n,S² of mesons with high spin S or high radial excitation number n are expected, from semiclassical arguments, to grow linearly with S and n. We show that this behavior can be reproduced within a putative 5-dimensional theory holographically dual to QCD (AdS/QCD). With the assumption that such a dual theory exists and describes highly excited mesons as well, we show that an asymptotically linear m² spectrum translates into a strong constraint on the infrared behavior of that theory. In the simplest model which obeys such a constraint we find m_n,S²∼(n+S).