Leptogenesis in the minimal gauged U(1)$_{L_μ-L_τ}$ model and the sign of the cosmological baryon asymmetry

Abstract

The minimal gauged U(1) Lµ−Lτ model is a simple extension of the Standard Model and has a strong predictive power for the neutrino sector. In particular, the mass spectrum and couplings of heavy right-handed neutrinos are determined as functions of three neutrino Dirac Yukawa couplings, with which we can evaluate the baryon asymmetry of the Universe generated through their decay, i.e., leptogenesis. In this letter, we study leptogenesis in the minimal gauged U(1) Lµ−Lτ model. It turns out that the sign of the resultant baryon asymmetry for the case with the Dirac CP phase, δ, larger than π is predicted to be opposite to that for δ < π. In addition, if lepton asymmetry is dominantly produced by the decay of the lightest right-handed neutrino, then the correct sign of baryon asymmetry is obtained for δ > π, which is favored by the current neutrino-oscillation experiments, whilst the wrong sign is obtained for δ < π. We further investigate a non-thermal leptogenesis scenario where the U(1) Lµ−Lτ breaking field plays the role of inflaton and decays into right-handed neutrinos, as a concrete example. It is found that this simple framework offers a successful inflation that is consistent with the CMB observation. We then show that the observed amount of baryon asymmetry can be reproduced in this scenario, with its sign predicted to be positive in most of the parameter space.

Heavy neutral leptons in gauged U(1) L µ −L τ at muon collider*

“…Three heavy neutral leptons with charge are introduced to generate tiny neutrino masses. Predicting type C of the two-zero minor [46,47], the minimal model with only one scalar singlet , which carries charge , is now tightly constrained by the neutrino oscillation data and the sum of light neutrino masses [48,49]. Thus, the second scalar singlet with charge is also employed to reduce the above conflict [50].…”

Maximally self-interacting dark matter: models and predictions

“…7 The charge of Φ determines the neutrino mass matrix by the see-saw mechanism [73][74][75][76]. Our choice is a minimal viable one [77] (see also Appendix C) and may explain the baryon asymmetry of the Universe [78] through the leptogenesis [79][80][81][82]. 8 Hereafter we assume the CP symmetry to restrict the Yukawa coupling.…”