A bridge to new physics: proposing new — and reviving old — explanations of aμ
Guilherme Guedes, Pablo Olgoso
Abstract
A bstract The 4 . 2 σ tension in the combined measurement of the anomalous magnetic moment of the muon, a μ , and the Standard Model prediction strongly suggests the existence of beyond the Standard Model physics. Following the Standard Model Effective Field Theory approach, we study a particular topology, the bridge diagram, which gives a chirally enhanced contribution to a μ . We classify all possible 2- and 3-field SM extensions that can generate this contribution and present the full a μ result for them. Within our approach, we find that several 2-field fermion-scalar extensions which had been previously discarded in the literature — when only the Yukawa-suppressed contribution was considered — can actually be viable models to explain the observed anomaly. Furthermore, the 3-field extensions which generate the bridge diagram represent a new class of models to account for a μ . We explore a particular 3-field extension which, beyond explaining a μ , can also account for the neutral B -meson anomalies and the Cabibbo angle anomaly. We present the full one-loop matching for this model and a one-loop phenomenological study.