TeV-scale seesaw mechanism with quintuplet fermions

Abstract

We propose a new seesaw model based on a fermionic hypercharge zero weak quintuplet in conjunction with an additional scalar quadruplet which attains an induced vacuum expectation value. The model provides both tree-level seesaw ∼ v 6 /M 5 and loop-suppressed radiative ∼ (1/16π 2 ) · v 2 /M contributions to active neutrino masses. The empirical masses m ν ∼ 10 −1 eV can be achieved with M ∼ TeV new states, accessible at the LHC. For 5 fb −1 of accumulated integrated luminosity at the LHC, there could be ∼ 500 doubly-charged Σ ++ or Σ ++ fermions with mass M Σ = 400 GeV, leading to interesting multilepton signatures. The neutral component of the fermion quintuplet, previously identified as a minimal dark matter candidate, becomes unstable in the proposed seesaw setup. The stability can be restored by introducing a Z 2 symmetry, in which case neutrinos get mass only from radiative contributions.

A model of radiative neutrino mass: with or without dark matter

“…Radiative corrections lift these mass degeneracies. For example, loops involving SM gauge bosons induce splittings of M F ++ − M F + ≃ 490 MeV, and M F + − M F 0 ≃ 163 MeV, among the components of F, leaving F 0 as the lightest state once loop-corrections are incorporated [41][42][43]. Similar splittings are induced for the components of φ [41].…”

“…They allow a generalization of the Type-III seesaw mechanism [44] that achieves neutrino mass via a low-energy effective operator of mass-dimension d = 9 [42,45,46]. Similarly they permit a generalized inverse seesaw mechanism [48].…”

Two viable large scalar multiplet models with aZ2symmetry

“…For n = 7, the scalar potential preserves an accidental Z 2 symmetry under which the large multiplet is odd; for n = 5 or 9, such a Z 2 symmetry is not automatic but can be imposed by hand [18]. These models are viable and have been considered in Refs.…”

Two-loop radiative seesaw model with inert triplet scalar field

“…For an example, the SM Higgs boson search in the diphoton mode h → γγ at Large Hadron Collider (LHC) is shown that its signal strength is 1.65±0. 24 at ATLAS [1,2] and 1.6±0.4 at CMS [3]. For another example, the existence of non-baryonic dark matters (DMs), which cannot be included in SM, dominates about 23% from the CMB observation by WMAP [4].…”