Warped Penguins

TL;DR

This paper analyzes one-loop magnetic dipole operators in the Randall-Sundrum warped extra dimension model, calculating mu to e gamma branching ratios and exploring flavor bounds, finiteness, and the perturbative regime.

Contribution

It provides explicit calculations of one-loop magnetic dipole operators in the RS model, demonstrating their finiteness and analyzing flavor bounds without fine tuning.

Findings

One-loop magnetic dipole operators are finite in the RS model.

Flavor bounds depend on the anarchic Yukawa and KK scales.

A perturbative regime exists where one-loop results dominate.

Abstract

We present an analysis of the loop-induced magnetic dipole operator in the Randall-Sundrum model of a warped extra dimension with anarchic bulk fermions and an IR brane localized Higgs. These operators are finite at one-loop order and we explicitly calculate the branching ratio for mu to e gamma using the mixed position/momentum space formalism. The particular bound on the anarchic Yukawa and KK scales can depend on the flavor structure of the anarchic matrices. It is possible for a generic model to either be ruled out or unaffected by these bounds without any fine tuning. We quantify how these models realize this surprising behavior. We also review tree-level lepton flavor bounds in these models and show that these are are in mild tension with the penguin bounds from typical models with a 3 TeV Kaluza-Klein scale. Further, we illuminate the nature of the one-loop finiteness of these diagrams and show how to accurately determine the degree of divergence of a 5D loop diagram using both the 5D and KK formalism. This power counting can be obfuscated in the 4D Kaluza-Klein formalism and we explicitly point out subtleties that ensure that the two formalisms agree. Finally, we remark on the existence of a perturbative regime in which these one-loop results give the dominant contribution.