Connecting Dark Matter with  \(\mathrm{\Delta {N_{eff}}}\) in Dirac Scotogenic Model

We have proposed a Dirac scotogenic model to explain light neutrino mass. Light right handed neutrinos ( \(\nu _R\) ) are added to generate neutrino mass at one-loop level and they leaves the thermal bath at a early time and contribute to the effective degrees of freedom \((N_\textrm{eff})\) . Among the particle content, the lightest vector-like fermion ( \(N_1\) ) is behaving as a viable dark matter candidate. Meanwhile the charged component of the scalar doublet ( \(\phi \) ) lead the \(\mu \rightarrow e\gamma \) lepton flavour violating process and constrain the model parameter space.