Are we overlooking Lepton Flavour Universal New Physics in $b\to s\ell\ell$ ?

TL;DR

This paper explores the possibility that new physics in $b o s \, \ell\ell$ transitions may include both lepton-flavour universal and violating contributions, challenging previous assumptions and proposing new ways to identify the underlying theory.

Contribution

It introduces a comprehensive analysis allowing simultaneous LFUV and LFU new physics contributions, revealing new patterns and mechanisms to explain flavour anomalies.

Findings

Large LFUV and LFU NP contributions to $C_{10\mu}$ are possible.

Current and future observables like $Q_5$ are crucial for distinguishing NP scenarios.

Updated $R_K$ measurements remain key to confirming NP in flavour anomalies.

Abstract

The deviations with respect to the Standard Model (SM) that are currently observed in $b \to s \ell\ell$ transitions (the so-called flavour anomalies) can be interpreted in terms of different New Physics (NP) scenarios within a model-independent effective approach. We reconsider the determination of NP in global fits from a different perspective by removing one implicit hypothesis of current analyses, namely that NP is only Lepton-Flavour Universality Violating (LFUV). We examine the roles played by LFUV NP and Lepton-Flavour Universal (LFU) NP altogether, providing new directions to identify the possible theory beyond the SM responsible for the anomalies observed. New patterns of NP emerge due to the possibility of allowing at the same time large LFUV and LFU NP contributions to $C_{10\mu}$, which provides a different mechanism to obey the constraint from the $B_s \to\mu^+\mu^-$ branching ratio. In this landscape of NP, we discuss how to discriminate among these scenarios in the short term thanks to current and forthcoming observables. While the update of $R_K$ will be a major milestone to confirm the NP origin of the flavour anomalies, additional observables, in particular the LFUV angular observable $Q_5$, turn out to be central to assess the precise NP scenario responsible for the observed anomalies.