Dark matter in the type Ib seesaw model

Abstract

We consider a minimal type Ib seesaw model where the effective neutrino mass operator involves two different Higgs doublets, and the two right-handed neutrinos form a heavy Dirac mass. We propose a minimal dark matter extension of this model, in which the Dirac heavy neutrino is coupled to a dark Dirac fermion and a dark complex scalar field, both charged under a discrete Z2 symmetry, where the lighter of the two is a dark matter candidate. Focussing on the fermionic dark matter case, we explore the parameter space of the seesaw Yukawa couplings, the neutrino portal couplings and dark scalar to dark fermion mass ratio, where correct dark matter relic abundance can be produced by the freeze-in mechanism. By considering the mixing between the standard model neutrinos and the heavy neutrino, we build a connection between the dark matter production and current laboratory experiments ranging from collider to lepton flavour violating experiments. For a GeV mass heavy neutrino, the parameters related to dark matter production are constrained by the experimental results directly and can be further tested by future experiments such as SHiP.

Spontaneously stabilised dark matter from a fermiophobic U(1)′ gauge symmetry

“…Recently a new version of the type I seesaw mechanism, named as the type Ib seesaw mechanism [56], that can be just as testable as the low scale seesaw models above has been proposed, with the light neutrino masses originating from a new type of Weinberg operator involving two Higgs doublets and a Dirac heavy neutrino. It has been shown that the model cannot only be extended to include dark matter via a neutrino portal [57] but can also produce baryon asymmetry in a variant version [58]. However in this model, as in many such models, both the type Ib seesaw model itself and the inclusion of dark matter via a neutrino portal requires additional imposed discrete symmetries whose origin is not explained.…”

“…The charges of the fields in the model are summarised in table 1. The U (1) gauge symmetry, rather than any discrete Z 3 or Z 4 symmetries [57,58], is responsible for making the two Higgs doublets distinguishable and ensuring the type Ib seesaw structure. However, the U(1) symmetry does not completely take over the function of the discrete symmetries.…”

“…Prompted by one of the motivations of the type Ib seesaw mechanism, the Dirac neutrino is assumed to be around 1-100 GeV scale, where a testable dark matter model compatible with leptogenesis can be realised [57,58]. In this research, we focus on dark matter candidates above TeV scale, which means m χ M, M Φ i , 3 and the total averaged cross section reads…”

“…(2.11) and below. For sub-TeV scale Dirac neutrinos, the experimental upper bound on the largest Yukawa coupling is typically around 0.01 [57], therefore the active-sterile neutrino mixing can play an important role in indirect detection. At zero temperature limit, the cross section of DM annihilation is given by…”

Freezing In with lepton flavored fermions

“…We show that this choice is apt for the freeze-in mechanism. The neutrino sector on the other hand, is far more model dependent and could also lead to freeze-in mechanisms for certain models (see for example, [32,33]). We also address the issue of stability for charged lepton flavored DM and show that in the absence of total lepton number violating interactions, they can be absolutely stable.…”