Phenomenology of the Non-sterile Electroweak-scale Right-handed Neutrino Model

In this dissertation we have discussed the phenomenology of the non-sterile Electroweak-scale Right-handed Neutrino (EWν_R) model. In the EWν_R model, a right-handed neutrino can naturally acquire a mass around the electroweak scale Λ_{EW} ≈ 246 GeV. This model adds the mirror fermions and an interesting Higgs sector to the particle spectrum in the Standard Model. We demonstrate that a significant part of the parameter space in the original EWν_R model agrees with the precision constraints from the "Oblique Parameter" measurements. We then discuss the development of a minimal extension to the original EWν_R model. This extended EWν_R model includes the 125-GeV scalar that possesses "a dual nature": it can either be a SM-like Higgs OR an impostor very different from the SM Higgs, both of which have the signal strengths compatible with experiments.