Rare Decay of K Meson
  We investigate the rare decay processes of the K mesons, K_{L,S} -> \pi^0 \nu \bar{\nu} and K^{+} -> \pi^+ \nu \bar{\nu} in LR model with lepton family number being well conserved. In these processes, scalar operators (\bar{s}d)(\bar{\nu}_{\tau}\nu_{\tau}), which are derived from box diagram in LR model, play an important role due to an enhancement factor M_{K}/m_{s} in the matrix element $<\pi|\bar{s}d|K>$. It is emphasized that the K_{L} decay process through the scalar operator is not the CP violating mode, so the B(K_L -> \pi^{0} \nu \bar{\nu}) remains non-zero even in the CP conserved limit. We present the pion energy spectrum for these processes and discuss the effects of LR model. 
Y. Kiyo, T. Morozumi and M. Tanimoto