Lepton-number violation and massless nonorthogonal neutrinos

Mixing between light and heavy neutrinos can induce lepton-flavor and total-lepton-number violation in the light sector, even if the light neutrino masses are zero or extremely small, because the states actually produced in weak processes are generally nonorthogonal. We develop the formalism for describing such nonorthogonal neutrinos and explore the phenomenological implications for neutrino ``oscillation'' experiments, the solar-neutrino problem, constraints from universality and other charged- and neutral-current experiments, {μ}{→}e{γ}, and {Δ}L=±{}2 effects in muon decay and neutrinoless double-beta decay.