The Impact of Flavour Changing Neutral Gauge Bosons on B->X_s gamma

TL;DR

This paper investigates how new heavy neutral gauge bosons, such as Z', influence the rare B->X_s gamma decay, introducing novel contributions and mixing effects that could also impact other fermionic processes.

Contribution

It identifies two new contributions to B->X_s gamma decay from heavy neutral gauge bosons and calculates the first QCD mixing effect involving these bosons.

Findings

New one-loop contributions from gauge bosons and exotic quarks.

First calculation of QCD mixing of neutral current operators.

Potential impact on various fermion decay processes.

Abstract

The branching ratio of the rare decay B->X_s gamma provides potentially strong constraints on models beyond the Standard Model. Considering a general scenario with new heavy neutral gauge bosons, present in particular in Z' and gauge flavour models, we point out two new contributions to the B->X_s gamma decay. The first one originates from one-loop diagrams mediated by gauge bosons and heavy exotic quarks with electric charge -1/3. The second contribution stems from the QCD mixing of neutral current-current operators generated by heavy neutral gauge bosons and the dipole operators responsible for the B->X_s gamma decay. The latter mixing is calculated here for the first time. We discuss general sum rules which have to be satisfied in any model of this type. We emphasise that the neutral gauge bosons in question could also significantly affect other fermion radiative decays as well as non-leptonic two-body B decays, epsilon'/epsilon, anomalous (g-2)_mu and electric dipole moments.