CPviolations in lepton number violation processes and neutrino oscillations

We examine the constraints on the Maki-Nakagawa-Sakata (MNS) lepton mixing matrix from present and future experimental data of the neutrino oscillation and lepton number violation processes. We introduce a graphical representation of the $\mathrm{CP}$ violation phases which appear in the lepton number violation processes such as neutrinoless double beta decay, the ${\mu }^{-}-e^{+}$ conversion, and the K decay, $K^{-}\to {\pi }^{+}{\mu }^{-}{\mu }^{-}.$ Using this graphical representation, we derive the constraints on the $\mathrm{CP}$ violation phases in the lepton sector.