Lepton Mass Hierarchy and Neutrino Oscillations

Starting from the symmetry of lepton flavor democracy, we propose and discuss a simple pattern for the mass generation and flavor mixing of the charged leptons and neutrinos. The three neutrino masses are nearly degenerate, and the flavor mixing angles can be calculated. The observed deficit of solar and atmospheric neutrinos can be interpreted as a consequence of the near degeneracy and large oscillations of $\nu_e$, $\nu_{\mu}$ and $\nu_{\tau}$ in the vacuum. Our {\it Ansatz} can also accommodate the cosmological requirement for hot dark matter and the current data on neutrinoless $\beta\beta$-decay.