Neutrino Masses from Loop-Induced Dirac Yukawa Couplings

TL;DR

This paper proposes a model where tiny neutrino masses are generated through one-loop induced Dirac Yukawa couplings involving charged scalars and right-handed neutrinos, avoiding lepton number violation.

Contribution

It introduces a simple, testable model with loop-induced Dirac neutrino masses using charged scalars and a softly-broken Z_2 symmetry, compatible with experimental constraints.

Findings

Neutrino masses can be explained without lepton number violation.

Model satisfies constraints from neutrino oscillations and lepton flavor violation.

Charged scalar decay patterns are testable at LHC and ILC.

Abstract

We consider a possibility to naturally explain tiny neutrino masses without the lepton number violation. We study a simple model with SU(2)_L singlet charged scalars (s_1^+, s_2^+) as well as singlet right-handed neutrino (nu_R). Yukawa interactions for Dirac neutrinos, which are forbidden at the tree level by a softly-broken Z_2 symmetry, are induced at the one-loop level via the soft-breaking term in the scalar potential. Consequently neutrinos obtain small Dirac masses after the electroweak symmetry breaking. It is found that constrains from neutrino oscillation measurements and lepton flavor violation search results (especially for mu to e gamma) can be satisfied. We study the decay pattern of the singlet charged scalars, which could be tested at the LHC and the ILC. We discuss possible extensions also, e.g. to introduce dark matter candidate.