On Flavourful Easter eggs for New Physics hunger and Lepton Flavour Universality violation

TL;DR

This paper investigates subtle signs of New Physics in B-meson decays using Bayesian global fits, revealing potential deviations from the Standard Model at around 3 sigma, and discusses the impact of hadronic uncertainties.

Contribution

It introduces a comprehensive Bayesian analysis of New Physics effects in B decays, considering hadronic uncertainties and lepton flavor universality violation, using recent experimental data.

Findings

Potential 3 sigma evidence for New Physics contributions

Hadronic uncertainties significantly affect the size of inferred New Physics

Leptonic axial currents could be as relevant as vector currents in explaining anomalies

Abstract

Within the standard approach of effective field theory of weak interactions for $\Delta B = 1$ transitions, we look for possibly unexpected subtle New Physics effects, here dubbed "flavourful Easter eggs". We perform a Bayesian global fit using the publicly available HEPfit package, taking into account state-of-the-art experimental information concerning these processes, including the suggestive measurements from LHCb of $R_{K}$ and $R_{K^{*}}$, the latter available only very recently. We parametrize New Physics contributions to $b \to s$ transitions in terms of shifts of Wilson coefficients of the electromagnetic dipole and semi-leptonic operators, assuming CP-conserving effects, but allowing in general for violation of lepton flavour universality. We show how optimistic/conservative hadronic estimates can impact quantitatively the size of New Physics extracted from the fit. With a conservative approach to hadronic uncertainties we find nonzero New Physics contributions to Wilson coefficients at the level of $\sim 3\sigma$, depending on the model chosen. Furthermore, given the interplay between hadronic contributions and New Physics effects in the leptonic vector current, a scenario with nonstandard leptonic axial currents is comparable to the more widely advocated one with New Physics in the leptonic vector current.