Abstract
We propose a B − L gauged extension of the Standard Model where light neutrino masses arise from type III seesaw mechanism. Unlike the minimal B − L model with three right handed neutrinos having unit lepton number each, the model with three fermion triplets is however not anomaly free. We show that the leftover triangle anomalies can be cancelled by two neutral Dirac fermions having fractional B − L charges, both of which are naturally stable by virtue of a remnant ℤ2× {mathbb{Z}}_2^{prime } symmetry, naturally leading to a two component dark matter scenario without any ad-hoc symmetries. We constrain the model from all relevant phenomenological constraints including dark matter properties. Light neutrino mass and collider prospects are also discussed briefly. Due to additional neutral gauge bosons, the fermion triplets in type III seesaw can have enhanced production cross section in collider experiment.
Highlights
Similar null results have been reported by collider experiments like the large hadron collider (LHC) [17] as well as indirect detection experiments putting stricter upper limits on DM annihilation to standard model (SM) particles [18], specially the charged ones which can lead to excess of gamma rays for weakly interacting massive particle (WIMP) type DM
Unlike type I seesaw scenario in U(1)B−L model where three right handed singlet neutrinos with B − L charge −1 each leads to cancellation of all anomalies without any need of additional chiral fermions, type III seesaw implementation leads to additional anomalies due to the non-trivial SU(2)L structure of triplet fermions
We show that a gauged U(1)B−L model with three fermion triplets required for type III seesaw can be anomaly free due to the presence of two neutral Dirac fermions having fractional B − L charges
Summary
We have discussed our model elaborately. As mentioned earlier, in this work our prime motivation is to have a multicomponent dark matter scenario where both dark matter candidates are stable by virtue of a single symmetry group. We have demanded an additional local U(1)B−L gauge invariance where B and L are denoting baryon and lepton numbers respectively of a particular field This introduces anomalies (both axial vector and gauge-gravitational anomalies) in the theory which can only be evaded by the inclusion of additional fermionic degrees of freedom. This has elaborately been discussed in the previous section. We have properly adjusted B − L charges of these φis such that only the Dirac mass terms among these singlet fermions are possible and more importantly the Dirac mass matrix is diagonal This results in two physical Dirac fermions out of these four chiral fermions which are simultaneously stable and both can be viable dark matter candidates. The Lagrangian of our present model invariant under the full symmetry group is given by
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