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

Understand

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.