K-meson neutrinoless double muon decay as a probe of neutrino masses and mixings

Recently an upper bound on the rate of the lepton number violating decay K --> mu (+)mu (+)pi (-) has been significantly reduced by the E865 experime nt 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 mix ings. We find that it is insensitive to the light (eV domain) and heavy (Ge V domain) neutrinos. However due to the effect of a resonant enhancement th is decay is very sensitive to neutrinos nu (j) in the mass region 245 MeV l ess than or equal to m(nuj) 389 less than or equal to MeV. Ar present exper imental sensitivity we deduce new stringent limits on the neutrino mixing m atrix element U-muj for neutrino masses in this region. (C) 2000 Elsevier S cience B.V. All rights reserved.