LFU violations in leptonic $\tau$ decays and B-physics anomalies

TL;DR

This paper analyzes lepton flavor universality violations in tau decays within models addressing B-physics anomalies, highlighting the impact of vector-like fermions on effective couplings and predicting measurable deviations in future experiments.

Contribution

It provides a complete analysis of LFU violations in tau decays in models with a specific gauge group, incorporating vector-like fermions and their effects on effective couplings.

Findings

Vector-like fermions cause sizable modifications to effective couplings.

Predicted a few per-mil decrease in W-tau coupling.

Deviations are within reach of future experiments.

Abstract

We present a complete analysis of Lepton Flavor Universality (LFU) violations in leptonic $\tau$ decays in motivated models addressing the $B$-physics anomalies, based on the $SU(4)\times SU(3)\times SU(2)\times U(1)$ gauge group. We show that the inclusion of vector-like fermions, required by $B$-physics data, leads to sizable modifications of the leading-log results derived within an Effective Field Theory approach. In the motivated parameter-space region relevant to the $B$-physics anomalies, the models predict a few per-mil decrease of the effective $W$-boson coupling to $\tau$, within the reach of future experiments.