Type I + II Seesaw Model in light of the New Neutrino Oscillation Measurements

Abstract

Global analysis of neutrino oscillation data slightly favors normal mass ordering. In this work, we investigate an extended scalar sector that naturally gives rise to a type I + II seesaw mechanism after spontaneous symmetry breaking and explore the interplay between collider physics and lepton flavor violation, adopting normal ordering. In particular, we focus on the rare muon decays $\mu \rightarrow e \gamma$ and $\mu \rightarrow 3e$ and the same-sign dilepton searches at LHC, a canonical signature of a doubly charged scalar. We conclude that neither the precise value of the sum of the neutrino masses, taken from DESI data that favors $\sum m_\nu=0.07$~eV, nor alternative cosmological fits which prefer a more relaxed limit $\sum m_\nu=0.1$~eV, significantly changes the theoretical prediction for these rare decays. However, we observe an interesting interplay between collider physics and lepton flavor violation depending on the choices of the vacuum expectation value of the triplet scalar. In particular, we find that $\mu \rightarrow 3e$ is more constraining than $\mu \rightarrow e\gamma$, and the $\mu \rightarrow 3e$ decay can yield a lower mass limit of $3$~TeV on the doubly charged scalar, surpassing current LHC constraint.