# B-decay discrepancies after Moriond 2019

## TL;DR

Recent measurements of B decay ratios suggest potential new physics, favoring models with lepton flavor universality violation, especially involving semi-leptonic Wilson coefficients and leptoquark scenarios, with some models nearing exclusion limits.

## Contribution

The paper provides a comprehensive analysis of B decay anomalies post-Moriond 2019, highlighting the preference for semi-leptonic new physics contributions and the viability of the U_1 leptoquark model.

## Key findings

- Data favors new physics in semi-leptonic Wilson coefficients.
- A muonic contribution with C_9 = -C_10 is preferred.
- LFU shifts in C_9 improve fit and can originate from high-scale operators.

## 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.