We have derived new upper limits on several products (two at a time) of
lepton number violating λ′-type couplings from the consideration of
ΔS=2 and ΔB=2 box graphs. Each box contains one scalar
lepton and one W-boson or one charged-Higgs-boson as internal lines. Most of
these bounds are more stringent than previously obtained. Some of these product
couplings drive KL (and some other Bd) decays to two charged leptons at
enhanced rates. Some of them can explain the rare K+→π+ννˉ
event recently observed at BNL.Comment: Latex, 6 pages, no figures; revised and published version with minor
changes in the Table caption and a few cosmetic changes in the tex