Phenomenological consequences of singlet neutrinos

In this paper, we study the phenomenology of right-handed neutrino isosinglets. We consider the general situation where the neutrino masses are not necessarily given by ${\mathit{m}}_{\mathit{D}}^2$/M, where ${\mathit{m}}_{\mathit{D}}$ and M are the Dirac and Majorana mass terms, respectively. The consequent mixing between the light and heavy neutrinos is then not suppressed, and we treat it as an independent parameter in the analysis. It turns out that μ-e conversion is an important experiment in placing limits on the heavy mass scale (M) and the mixing. Mixings among light neutrinos are constrained by neutrinoless double-β decay, as well as by solar and atmospheric neutrino experiments. Detailed one-loop calculations for lepton-number-violating vertices are provided.