Connecting Light Dirac Neutrinos to a Multi-component Dark Matter Scenario in Gauged $B-L$ Model

TL;DR

This paper introduces a gauged B-L model where light Dirac neutrinos naturally acquire sub-eV masses and are linked to a multi-component dark matter sector stabilized by residual symmetries, with cosmological constraints shaping the parameter space.

Contribution

It presents a novel gauged B-L extension with Dirac neutrinos and multiple dark matter candidates, connecting neutrino mass generation to dark matter stability without extra global symmetries.

Findings

Neutrinos are Dirac particles with sub-eV masses in the model.

Dark matter stability is ensured by residual Z2 x Z'2 symmetries.

Cosmological data constrains the dark matter parameter space due to right-handed neutrino thermalisation.

Abstract

We propose a new gauged $B-L$ extension of the standard model where light neutrinos are of Dirac type, naturally acquiring sub-eV mass after electroweak symmetry breaking, without any additional global symmetries. This is realised by choosing a different $B-L$ charge for right handed neutrinos than the usual $-1$ so that the Dirac Yukawa coupling involves an additional neutrinophilic scalar doublet instead of the usual Higgs doublet. The model can be made anomaly free by considering four additional chiral fermions which give rise to two massive Dirac fermions by appropriate choice of singlet scalars. The choice of scalars not only helps in achieving the desired particle mass spectra via spontaneous symmetry breaking, but also leaves a remnant $Z_2 \times Z'_2$ symmetry to stabilise the two dark matter candidates. Apart from this interesting link between Dirac nature of light neutrinos and multi-component dark matter sector, we also find that the dark matter parameter space is constrained mostly by the cosmological upper limit on effective relativistic degrees of freedom $\Delta N_{\rm eff}$ which gets enhanced in this model due to the thermalisation of the light right handed neutrinos by virtue of their sizeable $B-L$ gauge interactions.