  We discuss the necessity of a right-handed Weyl neutrino due to the
vector-like phenomenon of the regularized Standard Model. It is shown that this
right-handed neutrino is decoupled from low energies as a free particle, and
Dirac neutrino masses are very small. We suggest gauge-invariant couplings
between down quarks and charged leptons so that charged leptons acquire masses
without extra Goldstone modes. By examining Schwinger-Dyson equations for
lepton self-energy functions, we show that the neutrinos get their Dirac masses
via explicit symmetry breakings that attribute to the mixing between neutrinos
and charged leptons. An analysis of these Dyson equations gives the four
relationships between inter-generation mixing angles and lepton masses.
