Soft-Wall Stabilization

TL;DR

This paper introduces a class of five-dimensional soft-wall models with a dynamically generated infrared scale, addressing the hierarchy problem and allowing for both discrete and continuous spectra relevant to particle physics and holography.

Contribution

It presents a new class of soft-wall models with a dynamically determined IR scale, capable of producing realistic spectra including Regge trajectories and unparticle-like continua.

Findings

Achieves large UV/IR hierarchy without fine-tuning.

Models spectra with discrete levels or continuous spectra with a mass gap.

Provides a framework connecting holography, QCD, and beyond Standard Model physics.

Abstract

We propose a general class of five-dimensional soft-wall models with AdS metric near the ultraviolet brane and four-dimensional Poincar\'e 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.