IS LARGE LEPTON MIXING EXCLUDED

The original <(nu)over bar>(mu)-(or <(nu)over bar>(tau)-) energy spectrum from the gravitational collapse of a star has a larger average energy than the spectrum for <(nu)over bar>(e) since the opacity of <(nu)over bar>(e) exceeds that of <(nu)over bar>(mu) (or nu(tau)). Flavor neutrino conversion <(nu)over bar>(e)<-><(nu)over bar>(mu) induced by lepton mixing results in partial permutation of the original <(nu)over bar>(e) and <(nu)over bar>(mu) spectra. An upper bound on the permutation factor p less than or equal to 0.35 (99% C.L.) is derived using the data from SN 1987A and a range of models of the neutrino emission. The relation between the permutation factor and the vacuum mixing angle is established, which leads to the upper bound on this angle. The upper bound sin(2)2 theta>0.7-0.9 excludes the large mixing angle solutions of the solar neutrino problem: ''just-so'' and, partly, MSW, as well as part of the region of the nu(e)-nu(mu) oscillation space which could be responsible for the atmospheric muon neutrino deficit. These limits are sensitive to the predicted neutrino spectrum and can be strengthened as supernova models improve. <(nu)over bar>(mu)-