The Bearable Compositeness of Leptons

Michele Frigerio (1) , Marco Nardecchia (2) , Javi Serra (3) , Luca Vecchi (4)

1 L2C - Laboratoire Charles Coulomb
2 INFN, Sezione di Trieste - Istituto Nazionale di Fisica Nucleare, Sezione di Trieste
3 TUM - Technische Universität Munchen - Technical University Munich - Université Technique de Munich
4 EPFL - Ecole Polytechnique Fédérale de Lausanne

Partial compositeness as a theory of flavor in the lepton sector is assessed. We begin presenting the first systematic analysis of neutrino mass generation in this context, and identifying the distinctive mass textures. We then update the bounds from charged lepton flavor and CP violating observables. We put forward a U(1)$^{3}$ × CP symmetry of the composite sector, in order to allow the new physics to be not far above the TeV scale. This hypothesis effectively suppresses the new contributions to the electron EDM and μ → eγ, by far the most constraining observables, and results in a novel pattern of flavor violation and neutrino masses. The CP violation in the elementary-composite mixing is shown to induce a CKM phase of the correct size, as well as order-one phases in the PMNS matrix. We compare with the alternative possibility of introducing multiple scales of compositeness for leptons, that also allow to evade flavor and CP constraints. Finally, we examine violations of lepton flavor universality in B-meson semi-leptonic decays. The neutral-current anomalies can be accommodated, predicting strong correlations among different lepton flavors, with a few channels close to the experimental sensitivity.

Mots clés: Beyond Standard Model; Technicolor and Composite Models; Neutrino Physics; Effective Field Theories; lepton: composite; neutrino: mass; neutrino: mass generation; neutrino: mass: texture; CP: violation; CKM matrix; B: semileptonic decay; lepton: flavor: violation; lepton: universality: violation; lepton number: violation; electron: electric moment; numerical calculations; new physics

Domaines: Physique des Hautes Energies - Phénoménologie [hep-ph]

Michele Frigerio, Marco Nardecchia, Javi Serra, Luca Vecchi. The Bearable Compositeness of Leptons. Journal of High Energy Physics, 2018, 10, pp.017. ⟨10.1007/JHEP10(2018)017⟩. ⟨hal-01851263⟩