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