Regular Article - Theoretical Physics
Heavy neutral lepton corrections to SM boson decays: lepton flavour universality violation in low-scale seesaw realisations
Pôle Théorie, Laboratoire de Physique des 2 Infinis Irène Joliot Curie (UMR 9012), CNRS/IN2P3, 15 Rue Georges Clemenceau, 91400, Orsay, France
2 Jožef Stefan Institut, P.O. Box 3000, Jamova Cesta 39, 1001, Ljubljana, Slovenia
3 Laboratoire de Physique de Clermont (UMR 6533), CNRS/IN2P3, Univ. Clermont Auvergne, 4 Av. Blaise Pascal, 63178, Aubière Cedex, France
Accepted: 15 December 2023
Published online: 10 February 2024
We study lepton flavour universality violation in SM boson decays in low-scale seesaw models of neutrino mass generation, also addressing other electroweak precision observables. We compute the electroweak next-to-leading order corrections, which turn out to be important – notably in the case of the invisible decay width of the Z boson, for which the corrections can be as large as the current experimental uncertainty. As a well-motivated illustrative study case, we choose a realisation of the Inverse Seesaw mechanism, and discuss the complementary role of lepton flavour conserving, lepton flavour violating and precision observables, both in constraining and in probing such models of neutrino mass generation. Our findings suggest that invisible Z decays are especially important, potentially at the origin of the most stringent constraints for certain regimes of the Inverse Seesaw (while complying with charge lepton flavour violation and other electroweak precision tests). We also discuss the probing power of the considered observables in view of the expected improvement in experimental precision at FCC-ee.
© The Author(s) 2024
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