Abstract

Recently an upper bound on the rate of the lepton number violating decay K+ --> mu (+)mu (+)pi (-) has been significantly reduced by the E865 experiment at BNL and further improvement is expected in the near future. We study this process as a possible source of information on neutrino masses and mixings. We find that it is insensitive to the light (eV domain) and heavy (GeV domain) neutrinos. However due to the effect of a resonant enhancement this decay is very sensitive to neutrinos nu (j) in the mass region 245 MeV less than or equal to m(nuj) 389 less than or equal to MeV. Ar present experimental sensitivity we deduce new stringent limits on the neutrino mixing matrix element U-muj for neutrino masses in this region. (C) 2000 Elsevier Science B.V. All rights reserved.