Phenomenological Implications of The Electroweak-scale Right-handed Neutrino Model

In this thesis, we present the model of right-handed neutrinos at electroweak scale (EWnuR) and its extended version under two crucial tests by the electroweak precision measurements and the discovery of the 125 GeV SM-like Higgs boson. The key feature of the model is the existence of non-sterile electroweak scale right-handed neutrinos together with scalar triplets. We show that the EWnuR model with the new particle content satisfies well the constraint of the electroweak precision measurements through the contribution to the oblique parameters, S,T,U. Moreover, the 125 GeV SM-like Higgs discovery necessitates extending the minimal EWnuR model by adding one more complex scalar doublet and imposing a new symmetry. We present two very distinct scenarios in which the 125 GeV Higgs boson candidate of the model behaves like and unlike the SM one. In both cases, the signal strength of the 125 GeV candidate satisfies the experimental results of the LHC. The phenomenology of the heavy spin-zero states is also taken into account.