K-L,K-S ->pi pi nu(nu)over-bar decays within and beyond the standard model- art. no. 094026

The decays K-L,K-S-->pi (o)pi (o)nu<(<nu>)over bar> and K-L,K-S-->pi (+)pi (-)nu<(<nu>)over bar> involve the weak transition from a strange to a nonst range quark. Although they have considerably smaller branching ratios than those for the corresponding rare processes involving single pions, some may be more distinguishable experimentally from background processes and thus could provide another probe of the s-->d nu<(<nu>)over bar> transition. Usi ng the recent knowledge of the CKM matrix elements and measurements of rela ted processes, we give improved predictions for their branching ratios both within and beyond the standard model.