A naturally light dilaton

TL;DR

The paper addresses how a naturally light dilaton can emerge despite the non-genericity of a massless conformal mode. It combines a 4D effective-field-theory argument with a holographic AdS5 realization, showing that an exactly marginal coupling line (κ crossing zero) plus a slowly broken conformal invariance (β(λ)=εβ̄(λ)) yield a potential V(φ)=κ(λ(φ)) φ^4 with a suppressed dilaton mass m_phi^2 ~ O(ε). In the 5D model, the dilaton is the radion stabilized by a Goldberger–Wise–like mechanism without fine-tuning of the IR brane tension, and the perturbative ε>0 generates a small but nonzero quartic and radion mass, consistent with the 4D RG intuition. The work provides a dynamical framework linking conformal symmetry breaking, radion stabilization, and a near-vanishing dilaton potential, with implications for scalar-gravity cosmology and holographic phenomenology.

Abstract

Goldstone's theorem does not apply straightforwardly to the case of spontaneously broken scale invariance. We elucidate under what conditions a light scalar degree of freedom, identifiable with the dilaton, can naturally arise. Our construction can be considered an explicit dynamical solution to the cosmological constant problem in the scalar version of gravity.