$B$ Flavour Anomalies: 2021 Theoretical Status Report

TL;DR

This paper reviews the status of B flavour anomalies as of 2021, summarizing experimental data and exploring theoretical explanations including effective field theories and explicit models, and discussing their implications for new physics.

Contribution

It provides a comprehensive summary of the 2021 theoretical status of B flavour anomalies, integrating model-independent and explicit model approaches and exploring their broader implications.

Findings

Discrepancies with SM predictions in B decay observables.

Effective field theory and explicit models can explain anomalies.

Models may also address dark matter, muon g-2, and neutrino issues.

Abstract

At the present time, there are discrepancies with the predictions of the SM in several observables involving $b \to s \ell^+ \ell^-$ and $b \to c \ell^- {\bar\nu}_\ell$ decays. These are the $B$ flavour anomalies. In this review, we summarize the data as of Moriond 2021 and present theoretical new-physics 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, $(g-2)_\mu$, neutrino properties, and hadronic anomalies.