The Light Radion Window

TL;DR

This paper investigates models with a very light radion particle, exploring their theoretical construction, phenomenological constraints, and potential detectability, highlighting a wide open mass window for future experimental searches.

Contribution

It provides explicit models for a light radion and analyzes the experimental bounds, expanding the understanding of radion phenomenology in the 100 keV to 10 GeV range.

Findings

Weak bounds from SN 1987a and cosmology in certain parameter regions.

Much of the 100 keV to 10 GeV mass window remains unconstrained.

Models with suppressed couplings can evade current experimental limits.

Abstract

Inspired by the Contino-Pomarol-Rattazzi mechanism we explore scenarios with a very light (100 keV to 10 GeV) radion which could be associated with the suppression of the electroweak contribution to vacuum energy. We construct explicit, realistic models that realize this mechanism and explore the phenomenological constraints on this class of models. Compared with axion-like particles in this mass range, the bounds from SN 1987a and from cosmology can be much weaker, depending on the the mass of the radion and its coupling to other particles. With couplings suppressed by a scale lower than 100 TeV much of the mass window from 100 keV to 10 GeV is still open.