B-decay discrepancies after Moriond 2019

Abstract: Following the updated measurement of the lepton flavour universality (LFU) ratio R_K in B -> Kll decays by LHCb, as well as a number of further measurements, e.g. R_K* by Belle and B_s -> mu mu by ATLAS, we analyse the global status of new physics in b -> s transitions in the weak effective theory at the b-quark scale, in the Standard Model effective theory at the electroweak scale, and in simplified models of new physics. We find that the data continues to strongly prefer a solution with new physics in semi-leptonic Wilson coefficients. A purely muonic contribution to the combination C_9 = -C_10, well suited to UV-complete interpretations, is now favoured with respect to a muonic contribution to C_9 only. An even better fit is obtained by allowing an additional LFU shift in C_9. Such a shift can be renormalization-group induced from four-fermion operators above the electroweak scale, in particular from semi-tauonic operators, able to account for the potential discrepancies in b -> c transitions. This scenario is naturally realized in the simplified U_1 leptoquark model. We also analyse simplified models where a LFU effect in b -> sll is induced radiatively from four-quark operators and show that such a setup is on the brink of exclusion by LHC di-jet resonance searches.

• The paper finds that a muonic solution with C9 = -C10 successfully fits the B-decay anomalies observed in b→sℓℓ transitions.
• It employs global fits within WET and SMEFT frameworks to address branching ratio suppressions and angular observable deviations, accounting for hadronic uncertainties.
• The study supports new physics scenarios including simplified U1 leptoquark models and anticipates future constraints from LHC di-jet resonance searches.

Analysis of $B$-decay Discrepancies in the Context of New Physics

The paper analyzes discrepancies in $B$-decay processes, particularly focusing on recent data regarding $b\to s\ell\ell$ transitions. This research interprets the anomalies observed in $B$-decay measurements as potential indications of new physics beyond the Standard Model (SM). The study employs comprehensive global fits to various effective field theory frameworks, including the Weak Effective Theory (WET) at the $b$-quark scale and the Standard Model Effective Field Theory (SMEFT) above the electroweak scale, as well as considering potential simplified new physics models.

The anomalies in $B$-decays are categorized into four distinct areas:

1. Suppression of Branching Ratios in $b\to s\mu\mu$ Transitions: Observations show a consistent suppression across several exclusive decay modes through flavor-changing neutral current processes. The study notes that uncertainties in hadronic form factors contribute significantly to theoretical limitations in these processes.
2. Angular Observable Deviations in $B\to K^*\mu^+\mu^-$: Similar to the suppression of branching ratios, these angular discrepancies can also arise due to form factor uncertainties, albeit less severe than those affecting branching ratios.
3. Lepton Flavor Universality (LFU) Violation in $b\to s\ell\ell$ Transitions: The paper points out deviations from LFU in $R_K$ and $R_{K^*}$ measurements, while the theoretical uncertainties for these observables are minimal, making statistical fluctuation as a less favored explanation.
4. LFU in $b\to c\ell\nu$ Transitions: Apparent deviations are identified in the processes involving $c$-quark transitions, cemented by various independent experiments.

A notable conclusion is that modifications in the semi-leptonic Wilson coefficients, especially a muonic solution where $C_9 = -C_{10}$ provides a preferable fit for the data. This hypothesis is further supported by the potential renormalization effects induced by semi-tauonic operators at scales above the electroweak level. These scenarios are particularly compatible with the simplified $U_1$ leptoquark models.

Furthermore, the paper anticipates future constraints on LFU effects radiatively induced from four-quark operators as these might verge on exclusion by di-jet resonance searches conducted at the LHC.

In a broader exploration, the research contemplates the implications of these discrepancies on both experimental and theoretical levels. It speculates on the necessity of integrating additional data, potentially from Belle and future LHC runs, to corroborate the suggested new physics scenarios more convincingly.

In conclusion, this academic investigation refines the understanding of $B$-decay anomalies by integrating complex data analyses within the framework of both model-independent and model-specific interpretations. The paper underscores the viability of SMEFT and WET approaches in elucidating new physics, thereby setting the stage for intriguing developments in ongoing and future experimental outputs. The results present a compelling narrative that steers away from traditional SM paradigms, offering a stratified insight into potential pathways that new physics could unfold within the landscape of particle interactions.