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+→μ+μ+π− 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 νj in the mass region 245 MeV⩽mνj⩽389 MeV. At present experimental sensitivity we deduce new stringent limits on the neutrino mixing matrix element Uμj for neutrino masses in this region.