Lepton flavour violation in RS models with a brane- or nearly brane-localized Higgs

TL;DR

This paper provides a comprehensive 5D quantum-field-theoretical analysis of charged lepton flavor violation in Randall-Sundrum models, including various Higgs localizations, and derives constraints on model parameters from experimental bounds.

Contribution

It presents the first complete calculation of the flavor-violating electromagnetic dipole operator in RS models, considering different Higgs localizations and their effects on lepton flavor violation.

Findings

KK scale lower limit around 2 TeV in minimal RS model

Constraints from mu -> e gamma and mu N -> e N are most stringent

First KK excitations are about 10 TeV, beyond current LHC reach

Abstract

We perform a comprehensive study of charged lepton flavour violation in Randall-Sundrum (RS) models in a fully 5D quantum-field-theoretical framework. We consider the RS model with minimal field content and a "custodially protected" extension as well as three implementations of the IR-brane localized Higgs field, including the non-decoupling effect of the Kaluza-Klein (KK) excitations of a narrow bulk Higgs. Our calculation provides the first complete result for the flavour-violating electromagnetic dipole operator in Randall-Sundrum models. It contains three contributions with different dependence on the magnitude of the anarchic 5D Yukawa matrix, which can all be important in certain parameter regions. We study the typical range for the branching fractions of mu -> e gamma, mu -> 3e, mu N -> e N as well as tau -> mu gamma, tau -> 3 mu and the electron electric dipole moment by a numerical scan in both the minimal and the custodial RS model. The combination of mu -> e gamma and mu N -> e N currently provides the most stringent constraint on the parameter space of the model. A typical lower limit on the KK scale T is around 2 TeV in the minimal model (up to 4 TeV in the bulk Higgs case with large Yukawa couplings), and around 4 TeV in the custodially protected model, which corresponds to a mass of about 10 TeV for the first KK excitations, far beyond the lower limit from the non-observation of direct production at the LHC.