Constraints on new physics from $$K \rightarrow \pi \nu {\bar{\nu }}$$ K→πνν¯

Abstract

Abstract We study generic effects of new physics on the rare decay modes $$K_L \rightarrow \pi ^0 \nu {\bar{\nu }}$$ KL→π0νν¯ and $$K^+ \rightarrow \pi ^+ \nu {\bar{\nu }}$$ K+→π+νν¯ . We discuss several cases: left-handed neutrino couplings; right handed neutrino couplings; neutrino lepton flavour violating (LFV) interactions; and $$\Delta I =3/2$$ ΔI=3/2 interactions. The first of these cases has been studied before as it covers many new physics extensions of the standard model; the second one requires the existence of a new light (sterile) right-handed neutrino and its contribution to both branching ratios is always additive to the SM. The case of neutrino LFV couplings introduces a CP conserving contribution to $$K_L \rightarrow \pi ^0 \nu {\bar{\nu }}$$ KL→π0νν¯ which affects the rates in a similar manner as a right handed neutrino as neither one of these interferes with the standard model amplitudes. Finally, we consider new physics with $$\Delta I =3/2$$ ΔI=3/2 interactions to go beyond the Grossman-Nir bound. We find that the rare kaon rates are only sensitive to new physics scales up to a few GeV for this scenario.