Phenomenology of Dirac and Majorana type Heavy Neutral Leptons and their searches at the FCC-ee

Neutrinos in the Standard Model are massless particles, however neutrino oscillation experiments have demonstrated that neutrinos have masses. Beyond the Standard Model theories exist to introduce neutrino mass mechanisms. Some of these models do so by postulating the existence of additional particles, the heavy neutral leptons (HNLs). These particles can be of Dirac or Majorana type based on the specific model. In this thesis, theoretical computations show possible kinematical variables of final state particles that can provide discrimination between the Dirac vs Majorana nature of the HNLs and experimental simulations and analysis show the possibility of such discrimination within the context of their possible discovery at the FCC-ee experiment at CERN.