Abstract
The neutral component of an inert scalar multiplet with hypercharge can provide a stable dark matter particle when its real and imaginary parts have a splitting mass spectrum. Otherwise, a tree-level dark-matter-nucleon scattering mediated by the Z boson will be much above the experimental limit. In this paper we focus on a mixed inert scalar triplet dark matter scenario where a complex scalar triplet with hypercharge can mix with another real scalar triplet without hypercharge through their renormalizable coupling to the standard model Higgs doublet. We consider three specified cases that carry most of the relevant features of the full parameter space: (i) the neutral component of the real triplet dominates the dark matter particle, (ii) the neutral component of the complex triplet dominates the dark matter particle; and (iii) the neutral components of the real and complex triplets equally constitute the dark matter particle. Subject to the dark matter relic abundance and direct detection constraint, we perform a systematic study on the allowed parameter space with particular emphasis on the interplay among triplet-doublet terms and gauge interactions. In the presence of these mixed inert scalar triplets, some heavy Dirac fermions composed of inert fermion doublets can be utilized to generate a tiny Majorana neutrino mass term at one-loop level and realize a successful leptogenesis for explaining the cosmic baryon asymmetry.
Highlights
To the Higgs portal interaction and eventually decay into the SM species
In various seesaw extensions of the SM [12,13,14,15,16], some heavy fields, which are responsible for highly suppressing the neutrino masses, can decay to generate a lepton asymmetry converted to a baryon asymmetry by virtue of the sphaleron [17] processes
Thanks to the Yukawa couplings of the inert scalar triplets and fermion doublets to the SM lepton doublets, we can realize a radiative generation of the Majorana neutrino masses and a successful leptogenesis for the cosmic baryon asymmetry
Summary
Two inert scalars with different dimensions and/or hypercharges can mix with each other at the renormalizble level through their trilinear or quartic couplings with suitable Higgs scalars. We list the renormalizable, gauge-invariant terms for mixing the inert scalar singlet, doublet and triplet, in the presence of only one Higgs scalar, i.e. the SM Higgs doublet,. While models involving a stable DM arising from two mixed inert scalars have not received the same level of attention as those with pure scalar singlet or multiplets, both the singlet-doublet and singlet-triplet combinations have been considered previously [41, 42]. Take the Model I+II in Eq (2.1) as an example, the inert singlet χ and the real part ηR0 of the neutral component η0 of the inert doublet η mix after the electroweak symmetry breaking to produce two physical scalars, from which the lighter, proved to be the lightest among other states, emerges as the DM candidate. In the following of this paper, we will focus on the mixed inert scalar triplets, i.e. the model (2.6)
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