# Semi-leptonic $B$-physics anomalies: a general EFT analysis within $U(2)^n$ flavor symmetry

## TL;DR

This paper investigates recent anomalies in semi-leptonic B decays suggesting lepton flavor universality violation, using a general effective field theory with a U(2)^n flavor symmetry, and explores their consistency with other low-energy observables.

## Contribution

It introduces a comprehensive EFT framework with U(2)^n flavor symmetry to analyze B-physics anomalies and proposes a dynamical coupling preference to third-generation fermions for consistency.

## Key findings

- Anomalies can be explained with moderate fine-tuning.
- A dynamical coupling to third-generation fermions is compatible with observations.
- Identifies tau decay observables as potential tests for the new physics framework.

## Abstract

We analyse the recent hints of Lepton Flavor Universality violations in semi-leptonic $B$ decays within a general EFT based on a $U(2)^n$ flavor symmetry acting on the light generations of SM fermions. We analyse in particular the consistency of these anomalies with the tight constraints on various low-energy observables in $B$ and $\tau$ physics. We show that, with a moderate fine-tuning, a consistent picture for all low-energy observables can be obtained under the additional dynamical assumption that the NP sector is coupled preferentially to third generation SM fermions. We discuss how this dynamical assumption can be implemented in general terms within the EFT, and we identify a series of observables in $\tau$ decays which could provide further evidences of this NP framework.