The birds and the Bs in RS: the b to s gamma penguin in a warped extra dimension

TL;DR

This paper investigates how a warped extra dimension model affects b -> s gamma transitions, revealing significant new contributions to decay processes and potential deviations from Standard Model predictions in certain CP asymmetries.

Contribution

It provides the first detailed calculation of magnetic dipole operators in the Randall-Sundrum model with anarchic bulk fermions, highlighting new effects on b -> s gamma transitions and flavor observables.

Findings

Large contributions to left-handed b quark decays via Wilson coefficient C'_7.

Significant gluonic penguin contributions through renormalization group mixing.

Potential large enhancements in CP asymmetries in B decays.

Abstract

We calculate contributions to the photon and gluon magnetic dipole operators that mediate b -> s gamma and b -> d gamma transitions in the Randall-Sundrum model of a warped extra dimension with anarchic bulk fermions and a brane localized Higgs. Unlike the Standard Model, there are large contributions to the left-handed b quark decays, parameterized by the Wilson coefficient C'_7, due to the pattern of bulk fermion localization, and sizable contributions from the gluonic penguins, C(')_8, through renormalization group mixing. Further, unlike the Randall-Sundrum result for mu -> e gamma, the unprimed Wilson coefficients receive non-negligible contributions from the misalignment of the bulk fermion spectrum with the Standard Model flavor sector. We compare the size of effects and the constraints imposed by the branching ratios Br(B -> X_s gamma) and <Br(B -> X_d gamma)> within the minimal and the custodial model. Within the custodial framework, we study the effect on a number of benchmark observables and find that Br(B -> X_s mu^+ mu^-) and the forward-backward asymmetry in B -> K^* mu^+ mu^- remain close to their Standard Model predictions. On the other hand, there can be large enhancements of the time-dependent CP asymmetry in B -> K^* gamma and the transverse asymmetry A_T^(2).