Small neutrino masses from a decoupled singlet scalar field

초록

We propose a unified solution with Z4 discrete symmetry for small neutrino masses and stability of dark matter. The Standard Model is extended with an inert doublet scalar, a dark singlet scalar, a spurion scalar and right-handed neutrinos, which all transform nontrivially under Z4. After the Z4 symmetry is broken to Z2 by the VEV of the spurion, much below the mass scale of the dark singlet scalar, a small lepton number violating coupling for the inert doublet is generated at tree level, so small neutrino masses are obtained at one-loops for relatively light new fields. We discuss the important roles of the Z4 symmetry for neutrino masses, dark matter physics and thermal leptogenesis. © 2025 The Author(s)