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 $K^+\to \mu^+\mu^+\pi^-$ 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 $245{MeV}\leq m_{\nu_j}\leq 389$ MeV. At present experimental sensitivity we deduce new stringent limits on the neutrino mixing matrix element $U_{\mu j}$ for neutrino masses in this region. 
Claudio Dib, Vladimir Gribanov, Sergey Kovalenko and Ivan Schmidt