Violations of lepton-flavour universality in P -> l nu decays: a model-independent analysis

TL;DR

This paper investigates potential violations of lepton-flavour universality in meson decays using a model-independent effective theory approach, highlighting where observable effects could occur beyond the Standard Model.

Contribution

It provides a comprehensive analysis of lepton-flavour universality violations across different models and flavor-symmetry breaking patterns, emphasizing possible large effects in B meson decays.

Findings

Minimal Lepton Flavour Violation models predict effects too small for upcoming experiments.

Grand Unified models can produce large violations in B -> l nu decays.

Effects in Pi and K decays remain small across models.

Abstract

We analyse the violations of lepton-flavour universality in the ratios B(P -> l nu)/B(P -> l' nu) using a general effective theory approach, discussing various flavour-symmetry breaking patterns of physics beyond the SM. We find that in models with Minimal Lepton Flavour Violation the effects are too small to be observed in the next generations of experiments in all relevant meson systems (P = Pi, K, B). In a Grand Unified framework with a minimal breaking of the flavour symmetry, the effects remain small in Pi and K decays while large violations of lepton-flavour universality are possible in B -> l nu decays.