Double type-II seesaw scenario, baryon asymmetry, and dark matter for cosmice±excesses

Abstract

We construct a new realization of type-II seesaw for neutrino masses and baryon asymmetry by extending the standard model with one light and two heavy singlet scalars besides one Higgs triplet. The heavy singlets pick up small vacuum expectation values to give a suppressed trilinear coupling between the triplet and doublet Higgs bosons after the light singlet drives the spontaneous breaking of lepton number. The Higgs triplet can thus remain light and be accessible at the LHC. The lepton number conserving decays of the heavy singlets can generate a lepton asymmetry stored in the Higgs triplet to account for the matter-antimatter asymmetry in the Universe. We further introduce stable gauge bosons from a hidden sector, which obtain masses and annihilate into the Higgs triplet after spontaneous breaking of the associated non-Abelian gauge symmetry. With Breit-Wigner enhancement, the stable gauge bosons can simultaneously explain the relic density of dark matter and the cosmic positron/electron excesses. PACS numbers: 14.60.Pq, 98.80.Cq, 95.35.+d

Connections between the seesaw model and dark matter searches

“…We demon-strated this possibility in the simplest dark matter model where a real SM-singlet scalar acts as the dark matter. Our conclusion could be applied to other dark matter models (for instance, see [7,23] …”

Leptogenesis with TeV Scale WR

“…(4), the present model has a first stage seesaw suppression of the parameter κhσi in a natural way. Therefore, this two-step seesaw scheme can be called a double type-II seesaw mechanism [15]. Clearly, the double type-II seesaw mechanism now is also applied to the generation of the right-handed neutrino masses m R .…”

“…We use this symmetry to generate lepton asymmetry of the Universe. The source of lepton asymmetry, however, is not the decay of RHNs but rather the decay of new heavy SM singlet scalar bosons, as for instance in [15] with nonzero lepton number that couples two sets of lepton number carrying scalars, one set coupling to leptons and the other to fields that do not couple to leptons. The former acquire vacuum expectation values at very low scale to generate neutrino masses via type-II seesaw mechanism.…”

“…We extend the minimal quark seesaw LR model by adding B − L ¼ 2 Higgs triplets to generate small neutrino masses using type-II seesaw mechanism. The required smallness of the triplet VEV needed for this purpose arises from a two-step suppression of the VEVs [15] with no couplings smaller than ∼10 −5 (roughly the same order as the electron Yukawa in the SM).…”

Loop neutrino masses from d = 7 operator

“…Finally, we mention that we will also not consider d = 7 operators with additional singlets, see for example [21,22].…”