Radion Dynamics and Phenomenology in the Linear Dilaton Model

TL;DR

This paper studies the properties, interactions, and collider phenomenology of the radion in a 5D linear dilaton model derived from Little String Theory, highlighting its unique couplings and experimental constraints.

Contribution

It introduces a detailed analysis of the radion's wavefunctions, masses, and couplings, including effects of dilaton interactions and Higgs-radion mixing, within the linear dilaton framework.

Findings

Radion mass is of order the curvature scale.

Radion couples to SM fields and enhances photon decay modes.

Current LHC data constrains the radion parameter space.

Abstract

We investigate the properties of the radion in the 5D linear dilaton model arising from Little String Theory. A Goldberger-Wise type mechanism is used to stabilise a large interbrane distance, with the dilaton now playing the role of the stabilising field. We consider the coupled fluctuations of the metric and dilaton fields and identify the physical scalar modes of the system. The wavefunctions and masses of the radion and Kaluza-Klein modes are calculated, giving a radion mass of order the curvature scale. As a result of the direct coupling between the dilaton and Standard Model fields, the radion couples to the SM Lagrangian, in addition to the trace of the energy-momentum tensor. The effect of these additional interaction terms on the radion decay modes is investigated, with a notable increase in the branching fraction to photons. We also consider the effects of a non-minimal Higgs coupling to gravity, which introduces a mixing between the Higgs and radion modes. Finally, we calculate the production cross section of the radion at the LHC and use the current Higgs searches to place constraints on the parameter space.