Radion dynamics, heavy Kaluza-Klein resonances and gravitational waves

TL;DR

This paper investigates the radion phase transition in warped models, analyzing gravitational wave signals and updating bounds on Kaluza-Klein resonance masses using recent gravitational wave data.

Contribution

It introduces a novel formulation for the radion effective potential that includes backreaction, details the radion spectrum evaluation, and updates bounds on Kaluza-Klein masses from gravitational wave observations.

Findings

Gravitational waves from radion phase transition can probe Kaluza-Klein masses up to 10^9 TeV.

O3 LIGO/Virgo data constrains models with Kaluza-Klein masses between 10^4 and 10^7 TeV.

The study refines the radion spectrum evaluation and accounts for finite lifetime effects in sound wave spectra.

Abstract

We study the confinement/deconfinement phase transition of the radion field in a warped model with a polynomial bulk potential. The backreaction of the radion on the metric is taken into account by using the superpotential formalism, while the radion effective potential is obtained from a novel formulation which can incorporate the backreaction. The phase transition leads to a stochastic gravitational wave background that depends on the energy scale of the first Kaluza-Klein resonance, $m_{\textrm{KK}}$. This work completes previous studies in the following aspects: i) we detail the evaluation of the radion spectrum; ii) we report on the mismatches between the thick wall approximation and the numerical bounce solution; iii) we include a suppression factor in the spectrum of sound waves accounting for their finite lifetime; and, iv) we update the bound on $m_{\textrm{KK}}$ in view of the O3 LIGO and Virgo data. We find that the forthcoming gravitational wave interferometers can probe scenarios where $m_{\textrm{KK}} \lesssim 10^9$ TeV, while the O3-run bounds rule out warped models with $10^4 \textrm{TeV} \lesssim m_{\textrm{KK}} \lesssim 10^7$ TeV exhibiting an extremely strong confinement/deconfinement phase transition.