Four-Neutrino Scenarios
The main features of four-neutrino 3+1 and 2+2 mixing schemes are reviewed, after a discussion on the necessity of at least four massive neutrinos if the solar, atmospheric and LSND anomalies are due to neutrino oscillations. Complete list of references on four-neutrino mixing at http://www.to.infn.it/~giunti/neutrino