Non-decoupling and lepton number violation in left-right models

We argue that large non-decoupling effects of heavy neutrinos can appear naturally in manifestly left-right symmetric models due to the minimization conditions of the scalar potential and the structure of vev's imposed by phenomenology. We derive constraints on off-diagonal light-heavy and heavy-heavy neutrino mixings from the searches for lepton violating decays mu --> e gamma, mu --> ee(-)e(+) and mu - e conversion in nuclei. The most stringent limits come from the latter process ee e because its amplitude shows a quadratic non-decoupling dependence on the heavy neutrino mass. Due to the suppression of right-handed currents by the large W-R mass the present experiments are not sensitive to the intergenerational mixings between heavy neutrinos if M(WR) > 200 TeV.