Impacts on searching for signatures of new physics from K^+ to π^+ ν bar{ν} decay

Impacts on new physics search from $\bbbar, \kkbar$ mixings and the rare decay $\kplusdecay$ are discussed. We show that, in a certain class of new physics models, the extra contributions to those processes can be parametrized by its ratio to the standard model (SM) contribution with the common CKM factors. We introduce two ratios to measure the new physics contributions, $R_1$ for $\xd$ and $\ek$ parameters, and $R_2$ for $\kplusdecay$ decay. Then, the experimentally allowed region for the new physics contributions can be given in terms of $R_1, R_2$ and the CP violating phase $\delta$ of the CKM matrix. We find constraints on $R_1$ and $\cosd$ by taking account of current experimental data and theoretical uncertainties on $\bbbar$ and $\kkbar$ mixings. We also study impacts of future improved measurements on ($R_1,R_2,\cosd$) basis. As typical examples of new physics models, we examine contributions to those processes in the minimal supersymmetric SM and the two Higgs doublet model.