Charged lepton flavor violating processes in neutrinophilic Higgs + seesaw model

Naoyuki Haba,Toshifumi Yamada,Tsuneharu Omija

doi:10.1093/ptep/ptaa089

Abstract

Abstract We investigate charged lepton flavor violating (CLFV) processes in the “neutrinophilic Higgs + seesaw model”, in which right-handed neutrinos couple only with an extra Higgs field which develops a tiny vacuum expectation value and the right-handed neutrinos also have Majorana mass. The model realizes a seesaw mechanism around TeV scale without extremely small Dirac Yukawa couplings. A phenomenological feature of the model is CLFV processes induced by loop diagrams of the charged scalar particles and heavy neutrinos. Therefore, first we constrain the model’s parameter space from the search for $\mu\to e\gamma$. Next, we predict the branching ratios of other CLFV processes including the $\mu\to3e$, $\mu+{\rm Al}\to e+{\rm Al}$, $\mu+{\rm Ti}\to e+{\rm Ti}$, $Z\to e\mu$, $Z\to e\tau$, $Z\to \mu\tau$, $h\to e\tau$ and $h\to\mu\tau$ processes, and discuss their detectability in future experiments.

Highlights

The origin of the smallness of the neutrino mass is one of the prime open questions in particle physics
One candidate solution to the above mystery is the neutrinophilic Two Higgs Doublet Model [1], where there is an extra Higgs doublet called “neutrinophilic Higgs”) that couples to the lepton doublets and right-handed neutrinos while the coupling of the Standard Model (SM) Higgs doublet to right-handed neutrinos is forbidden by a Z2 symmetry, and the smallness of the vacuum expectation value (VEV) of the neutrinophilic Higgs explains the smallness of the neutrino mass
We have investigated the neutrinophilic Higgs+seesaw model, in which right-handed neutrinos couple only with an extra Higgs field that develops a tiny VEV and have Majorana mass, and which realizes the low-scale seesaw naturally

Summary

Introduction

The origin of the smallness of the neutrino mass is one of the prime open questions in particle physics. [6] has studied CLFV processes in the neutrinophilic Two Higgs Doublet Model, but in that work, the Majorana mass term is not considered and the neutrinos are purely Dirac particles. Our work extends it by introducing Majorana mass for right-handed neutrinos. We assume that λ5 is suppressed as |λ5| ≪ 8π2mν|Mk|/|(YD)αi|2v2 and |λ5| ≪ 8π2mνm22/|(YD)αi|2v2|Mk|, where mν denotes the mass scale of active neutrinos and v ≃ 246 GeV It follows that, unlike the model of Ref. The quantity 3i=1(YD)ei fi (YD† )ie is always real and no electric dipole moment arises in the model

Branching Ratios of Charged Lepton Flavor Violating Processes

Γcapture peEem3μα3G2F 8π2Z

Numerical Study

Assumptions on the Model Parameters

Prediction on Charged Lepton Flavor Violating Processes

Summary