K -> pi nu nubar from standard to new physics

Abstract

Flavour changing neutral current decays are a very sensitive test of the standard model and its extensions. In particular the decay K -> pi nu nubar constitutes a clean way to provide constraints, independent of long distance effects. Motivated by the recent experimental data of the E787 and E865 collaborations and by the difference between the standard model prediction and data, we consider in detail new physics scenarios such as the minimal supersymmetric standard model and R-parity violating supersymmetry. We begin with analysing the impact of new measurements on the standard model result obtaining B(K^+ -> pi^+ nu nubar)=(8.18 +/- 1.22) x 10^(-11). Predictions for other rare kaon decays are discussed, too. Our results allow to improve the limits on R-parity violating couplings with respect to previous analyses.