Soft-wall stabilization

Abstract

We propose a general class of five-dimensional (5D) soft-wall models with AdS metric near the ultraviolet brane and 4D Poincaré invariance, where the infrared scale is determined dynamically. A large UV/IR hierarchy can be generated without any fine-tuning, thus solving the electroweak/Planck scale hierarchy problem. Generically, the spectrum of fluctuations is discrete with a level spacing (mass gap) provided by the inverse length of the wall, similar to RS1 models with standard model fields propagating in the bulk. Moreover, two particularly interesting cases arise. They can describe: (a) a theory with a continuous spectrum above the mass gap, which can model unparticles corresponding to operators of a CFT where the conformal symmetry is broken by a mass gap; and (b) a theory with a discrete spectrum provided by linear Regge trajectories as in AdS/QCD models.