$B$ Flavour Anomalies: 2021 Theoretical Status Report

Abstract

At the present time, there are discrepancies with the predictions of the SM in several observables involving b → s + − and b → c − ν decays. These are the B flavour anomalies. In this review, we summarize the data as of Moriond 2021 and present theoretical newphysics explanations from both a model-independent effective-field-theory point of view and through the building of explicit models. Throughout, we stress the complementarity of these two approaches. We also discuss combined explanations of both B anomalies, and present models that also explain other problems, such as dark matter, (g − 2) µ , neutrino properties, and hadronic anomalies.

Challenges for the 3-3-1 models

“…Although it is not clear at all if the latter anomalies will be confirmed in the near future, we have to pay attention for them [9].…”

Hyperon production in quasielastic $\barν_τ-$nucleon scattering

“…While in the case of b −→ clν l decays, all the three collaborations [37] have reported the ratio of the branching fraction in l = τ mode to l = µ mode, which challenge LFU at the level of four standard deviation. This has led to extensive theoretical work in constructing the models of new physics (NP) going beyond the standard model (BSM) to explain these experimental results on LFUV in the b quark sector [48][49][50]. In view of these developments in b quark sector, it is natural to apply these theoretical models [48][49][50] in the medium heavy quark sector involving c and s quarks decays like c −→ slν l , c −→ dlν l , s −→ ulν l , s −→ dl l and critically study the LFUV effects and search for them experimentally [51][52][53][54].…”

“…This has led to extensive theoretical work in constructing the models of new physics (NP) going beyond the standard model (BSM) to explain these experimental results on LFUV in the b quark sector [48][49][50]. In view of these developments in b quark sector, it is natural to apply these theoretical models [48][49][50] in the medium heavy quark sector involving c and s quarks decays like c −→ slν l , c −→ dlν l , s −→ ulν l , s −→ dl l and critically study the LFUV effects and search for them experimentally [51][52][53][54]. While these studies are being pursued with some interest, the need for further efforts in this direction has been emphasized recently [34].…”

Explaining the $b \to s \ell^+ \ell^-$ anomalies in $Z^\prime$ scenarios with top-FCNC couplings

“…The flavour-changing neutral current (FCNC) processes are sensitive to possible contributions from heavy mediators and provide a complementary way to direct searches for new physics (NP) at high-energy frontiers. While there is so far no direct evidence for NP at the LHC, recent measurements of the rare b → s + − decays exhibit several interesting discrepancies from the Standard Model (SM) predictions of the branching ratios, the angular distributions, and the lepton flavour universality (LFU) ratios [1][2][3][4].…”

“…the global tension in the b → s + − decays has motivated a lot of NP interpretations [1][2][3][4]. In this respect, one of the most popular NP explanations are models with an extra heavy vector Z boson.…”