Constraints on new physics from K→πν(ν)over-bar -: art. no. 093003

We study constraints on new physics from the recent measurement of Br(K+-->pi(+)nu(nu) over bar) by the E787 and E949 Collaborations. In our analysis, we consider two models of new physics: (a) extra down-type singlet quark model and (b) R-parity violating minimal supersymmetric standard model. We find that K+-->pi(+)nu(nu) over bar along with other processes such as K-L-->mu(+)mu(-),epsilon(')/epsilon provide useful bounds on the parameter U-sd, characterizing the off-diagonal Z-d-(s) over bar coupling of model (a). The bounds on Re(U-sd) from (K-L-->mu(+)mu(-))(SD) and Im(U-sd) from epsilon(')/epsilon are so tight that the branching ratio of K+-->pi(+)nu(nu) over bar can exceed the standard model value by at most a factor of 2. For model (b), we also obtain stringent bounds on certain combinations of the product of two lambda(ijk)(') couplings originating from L number-violating operator L(i)Q(j)D(k)(c) using K+-->pi(+)nu(nu) over bar and K-L-->mu(+)mu(-) processes. Even with the stringent constraints on U-sd [in model (a)] and on products of two R couplings [model (b)], we find that the branching ratio B(K-L-->pi(0)nu(nu) over bar) can be substantially different in both of the above models from those predicted in the standard model.