Effective theory of light Dirac neutrino portal dark matter with observable N eff
Abstract
We study the possibility of light Dirac neutrino portal dark matter (DM) in an effective field theory setup. Dirac nature of light neutrino automatically includes its right chiral part R which, in our setup, also acts like a portal between DM and the standard model (SM) particles. Considering a Dirac fermion singlet DM stabilized by an unbroken Z2 symmetry, we write down all possible dimension-6 effective operators involving DM-R as well as R-SM which conserve Z2, global lepton number and SM gauge symmetries. DM thermalization also ensures the thermalization of R, leading to enhanced effective relativistic degrees of freedom N eff, within reach of future cosmic microwave background (CMB) experiments. We study the complementarity among DM and CMB related observations for different Lorentz structures of effective operators. We also propose a UV complete gauged B-L symmetric model with Dirac neutrino portal dark matter.
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