Linear flavour violation and anomalies in B physics

Abstract

Abstract:We propose renormalizable models of new physics that can explain various anomalies observed in decays of B-mesons to electron and muon pairs. The new physics states couple to linear combinations of Standard Model fermions, yielding a pattern of flavour violation that gives a consistent fit to the gamut of flavour data. Accidental symmetries prevent contributions to baryon-and lepton-number-violating processes, as well as enforcing a loop suppression of new physics contributions to flavour violating processes. Data require that the new flavour-breaking couplings are largely aligned with the Yukawa couplings of the SM and so we also explore patterns of flavour symmetry breaking giving rise to this structure.

Loop effects of heavy new scalars and fermions in b → sμ + μ −

“…[60] that the anomalies in the b → sµ + µ − data and (g − 2) µ are explained by loop effects involving heavy new scalars and fermions that couple to the SM fermions via Yukawa-like interactions. In order to generate the Wilson coefficient C 9 , the new particles must couple to the left-handed SM quark doublets Q.…”

“…An explanation of the anomalies via loop effects, on the other hand, typically leads to correlated imprints on other observables like the anomalous magnetic moment of the muon (a µ ). It is thus appealing to investigate the possibility of a simultaneous solution of the flavor anomalies and the long-standing tension in (g − 2) µ at the loop level, for example by light Z bosons [39][40][41][42][43][44][45][46][47][48], leptoquarks [38,49,50] or new fermions and scalars [51][52][53][54][55][56][57][58][59][60][61] (see ref. [62] for a review on the situation in SUSY).…”

“…Whereas the emphasis in ref. [60] was on modelbuilding aspects and a particular higher-dimensional representation for the new particles under the SM gauge group, we explore in more detail the phenomenological consequences in a general class of models: we consider those representations which are realized in the SM (singlet, fundamental and adjoint) and study also the case of the fermions (scalars) being Majorana particles (real scalars).…”

“…[60], we introduce new heavy scalars and vector-like fermions in such a way that a one-loop box contribution to b → sµ + µ − is generated (see figure 1). As mentioned in the introduction, we will assume that the new particles only couple to lefthanded SM fermions.…”

Flavour anomalies after the R K ∗ measurement

“…The R K anomaly can be reproduced by one loop diagrams involving new scalars S and new fermions F with Yukawa couplings to SM fermions that allow for the Feynman diagram on the left in figure 7 [39,77] -see also ref. [78].…”