Muon polarization normal to theKL0→πμνdecay plane due to electromagnetic final-state interactions

Electromagnetic final-state interactions mimic $\mathrm{CP}$ violation in producing a nonzero muon polarization normal to the decay plane in $K_L^0\to \pi \mu \nu$ In this note I describe a calculation of this effect, and compare my result with the results of previously published calculations, which are in disagreement among themselves.