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.
Highlights
Besides the fundamental discovery of the Standard Model (SM) Higgs, the first run at the LHC had two clear outcomes
We show that a universal LFU new physics (NP) contribution, together with a lepton-flavor-universality violating (LFUV) NP contribution, gives rise to scenarios with a statistical significance at least as relevant as the ones identified in Ref. [19], against a common belief that the presence of such terms is not justified from the statistical point of view and should be dropped
Constrain LFUV NP contributions (CVil), whereas lepton-flavor dependent (LFD) observables will be sensitive to the sum of LFUV NP and LFU NP contributions (CUi þ CVil)
Summary
Besides the fundamental discovery of the Standard Model (SM) Higgs, the first run at the LHC had two clear outcomes. Combines the experimental data from LHC experiments (LHCb [5,6,7,8,9] and ATLAS [10] and CMS [11]) as well as the data from B factories (in particular, Belle [12,13]) together with theoretical input concerning long-distance hadronic contributions [14,15,16,17] They aim at extracting the value of the short-distance Wilson coefficients under given NP hypotheses and at comparing them with the SM expectations. [19], against a common belief that the presence of such terms is not justified from the statistical point of view and should be dropped This may help motivate the construction of new models including LFUV and LFU NP contributions. The UV completion of the SM may require significant contributions from two different sectors (LFU and LFUV) instead of a single one, as often assumed
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