Eur. Phys. J. C (2009) 64: 55-62
https://doi.org/10.1140/epjc/s10052-009-1130-z

Regular Article - Theoretical Physics

Violations of lepton-flavour universality in P→ℓ ν decays: a model-independent analysis

¹ Departament de Física Teòrica and IFIC, Universitat de València-CSIC, Apt. Correus 22085, 46071, València, Spain
² INFN, Laboratori Nazionali di Frascati, Via E. Fermi 40, 00044, Frascati, Italy

^* e-mail: gino.isidori@lnf.infn.it

Received: 3 July 2009
Published online: 19 September 2009

Abstract

We analyse the violations of lepton-flavour universality in the ratios ℬ(P→ℓ ν)/ℬ(P→ℓ ^′ ν) 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=π,K,B). In a Grand Unified framework with minimal breaking of the flavour symmetry, the effects remain small in π and K decays, while large violations of lepton-flavour universality are possible in B→ℓ ν decays.