Bounds on long-baseline (ν)over-bare→(ν)over-bare and ((ν)over-bar)μ→((ν)over-bar)e transition probabilities

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 us to obtain rather strong bounds on the long-baseline <(nu)over bar>(e) --> <(nu)over bar>(e) and <((nu))over bar>(mu) --> <((nu))over bar>(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.