Non-standard-model CP violation in ${\mathit{K}}_{\mathrm{\mu }3}$ decays as a method of probing for new physics

The transverse polarization of the muon (${\mathit{P}}_{\mathrm{\mu }}^{\mathrm{\perp }}$) in the decay ${\mathit{K}}^{+}$→${\mathrm{\pi }}^0$${\mathrm{\mu }}^{+}$${\nu }_{\mathrm{\mu }}$ is a very useful tool for studying CP violation because a detectable nonzero ${\mathit{P}}_{\mathrm{\mu }}^{\mathrm{\perp }}$ can only arise from physics beyond the standard model. Further, ${\mathit{P}}_{\mathrm{\mu }}^{\mathrm{\perp }}$ is interesting because it probes a different region of parameter space than many other CP-violating observables. To help justify an experimental search, we present three models which give ${\mathit{P}}_{\mathrm{\mu }}^{\mathrm{\perp }}$≳${10}^{\mathrm{-}3}$ and which are not contradicted by other experimental data. We also comment on K→πμμ decays.