Bounds on long-baseline nu_e->nu_e and nu_mu->nu_e transition probabilities

Abstract

We discuss long-baseline neutrino oscillations in the framework of the two 4-neutrino schemes which can accommodate all existing neutrino oscillation data. Negative results of short-baseline reactor and accelerator experiments allow to obtain rather strong bounds on the long-baseline nu_e->nu_e and nu_mu->nu_e transition probabilities. We consider in detail matter effects and show that the vacuum bounds are not substantially modified. We also comment on corresponding bounds in 3-neutrino scenarios.