%0 Journal Article %T New limits on effective Majorana neutrino masses from rare kaon decays %A K. Zuber %J Physics %D 2000 %I arXiv %R 10.1016/S0370-2693(00)00333-6 %X The rare kaon decay $K^+ \ra \pi^- \mu^+ \mu^+$ is violating lepton number by two units and is investigated within the context of Majorana neutrino masses. Using a new upper bound for this decay from E865 an upper limit on the effective Majorana mass term $\m_{\mu \mu} < 500$ GeV could be obtained. This is improving existing bounds by about one order of magnitude. Implications on heavy neutrinos are discusse d as well as future possibilities to improve limits on this as well as other elements of the Majorana m ass matrix are investigated. %U http://arxiv.org/abs/hep-ph/0003160v1