Multiscale confining dynamics from holographic RG flows

A bstract We consider renormalization group flows between conformal field theories in five (six) dimensions with a string (M-theory) dual. By compactifying on a circle (torus) with appropriate boundary conditions, we obtain continuous families of confining fourdimensional theories parametrized by the ratio Λ flow /Λ QCD , with Λ flow the scale at which the flow between fixed points takes place and Λ QCD the confinement scale. We construct the dual geometries explicitly and compute the spectrum of scalar bound states (glueballs). We find a ‘universal’ subset of states common to all the models. We comment on the modifications of these models, and the corresponding fine-tuning, required for a parametrically light ‘dilaton’ state to be present. We also comment on some aspects of these theories as probed by extended objects such as strings and branes.