On the Flavour Structure of Anomaly-free Hidden Photon Models

TL;DR

This paper investigates the flavor structure of anomaly-free hidden photon models, showing that such models inherently suppress flavor-changing couplings at tree level and exploring their experimental constraints and signatures.

Contribution

It demonstrates that anomaly cancellation constrains flavor-changing couplings in hidden photon models and analyzes how these models can be distinguished through neutrino and meson decay signatures.

Findings

Flavor-changing couplings are strongly suppressed at loop level.

Tree-level couplings are flavor conserving if CKM or PMNS matrices are reconstructed.

Constraints and future search projections for $U(1)_{B-3L_i}$ gauge bosons are provided.

Abstract

Extensions of the Standard Model with an Abelian gauge group are constrained by gauge anomaly cancellation, so that only a limited number of possible charge assignments is allowed without the introduction of new chiral fermions. For flavour universal charges, couplings of the associated hidden photon to Standard Model fermions are flavour conserving at tree-level. We show explicitly that even the flavour specific charge assignments allowed by anomaly cancellation condition lead to flavour conserving tree-level couplings of the hidden photon to quarks and charged leptons \emph{if} the CKM or PMNS matrix can be successfully reconstructed. Further, loop-induced flavour changing couplings are strongly suppressed. As a consequence, the structure of the Majorana mass matrix is constrained and flavour changing tree-level couplings of the hidden photon to neutrino mass eigenstates are identified as a means to distinguish the $U(1)_{B-L}$ gauge boson from any other anomaly-free extension of the Standard Model without new chiral fermions. We present a comprehensive analysis of constraints and projections for future searches for a $U(1)_{B-3L_i}$ gauge boson, calculate the reach of resonance searches in $B$ meson decays and comment on the implications for non-standard neutrino interactions.