Singlet-doublet fermion Dark Matter with Dirac neutrino mass, (g − 2)_μ and ∆N_eff

We study the possibility of generating light Dirac neutrino mass via scotogenic mechanism where singlet-doublet fermion Dark Matter (DM) plays non-trivial role in generating one-loop neutrino mass, anomalous magnetic moment of muon: (g − 2)_μ as well as additional relativistic degrees of freedom ∆N_eff within reach of cosmic microwave background (CMB) experiments. We show that the Dirac nature of neutrinos can bring interesting correlations within the parameter space satisfying the (g − 2)_μ, DM relic density and the effective relativistic degrees of freedom ∆N_eff. While we stick to thermal singlet-doublet DM with promising detection prospects, both thermal and non-thermal origin of ∆N_eff have been explored. In addition to detection prospects of the model at DM, (g − 2)_μ and other particle physics experiments, it remains verifiable at future CMB experiments like CMB-S4 and SPT-3G.