  We study generic effects of new physics on the rare decay modes $K_L \to
\pi^0 \nu \bar\nu$ and $K^+ \to \pi^+ \nu \bar\nu$. We discuss several cases:
left-handed neutrino couplings; right handed neutrino couplings; neutrino
lepton flavour violating (LFV) interactions; and $\Delta I =3/2$ 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 $K_L \to \pi^0 \nu
\bar\nu$ 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 $\Delta I =3/2$ 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.
