# Gauge-invariant implications of the LHCb measurements on Lepton-Flavour Non-Universality

## TL;DR

This paper analyzes recent LHCb measurements of $R_K$ and $R_{K^*}$ using SMEFT, revealing potential new physics effects that could be the first detectable dimension-six operators in the Standard Model.

## Contribution

It provides a model-independent SMEFT framework to interpret $b o s \, \ell\ell$ anomalies and sets a standard for future high-energy new physics analyses.

## Key findings

- Operators could be the first dimension-six terms detected experimentally.
- Combined $b\to s \ell\ell$ data shows >5 sigma deviation from SM.
- Constraints on SMEFT operators at low and high energies.

## Abstract

We study the implications of the recent measurements of $R_K$ and $R_{K^*}$ by the LHCb collaboration. We do that by adopting a model-independent approach based on the Standard Model Effective Field Theory (SMEFT), in which the dominant new physics effects are encoded in the coefficients of dimension-six operators respecting the full Standard Model (SM) gauge symmetry. After providing simplified expressions for $R_K$ and $R_{K^\ast}$, we determine the implications of the recent LHCb results for these observables on the coefficients of the SMEFT operators at low and high energies. We also take into account all $b\to s \ell\ell$ data, which combined lead to effective New Physics (NP) scenarios with SM pulls in excess of 5~$\sigma$. Thus the operators discussed in this paper would be the first dimension-six terms in the SM Lagrangian to be detected experimentally. Indirect constraints on these operators are also discussed. The results of this paper transcend the singularity of the present situation, and set a standard for future analyses in $b\to s$ transitions when the NP is assumed to lie above the electroweak scale.