An effective holographic approach to QCD

We describe a holographic approach to QCD where conformal symmetry is broken explicitly in the UV by a relevant operator ${\cal O}$. The operator maps to a 5d scalar field, the dilaton, with a massive term. Implementing also the IR constraint found by Gursoy, Kiritsis and Nitti, an approximate linear glueball spectrum is obtained which is consistent with lattice data. Finally, we describe the evolution of the model parameters with the conformal dimension of ${\cal O}$. This suggests a map between the QCD trace anomaly and the trace Ward identity of deformed conformal field theories.