T violation in K+→μ+νγ decay and supersymmetry

Measurement of the transverse muon polarization Pμperpendicular in the K+→μ+νγ decay will be attempted for the first time at the ongoing KEK E246 experiment and also at a proposed BNL experiment. We provide a general analysis of how Pμperpendicular is sensitive to the physical CP-violating phases in new physics induced four-Fermi interactions, and then we calculate the dominant contributions to Pμperpendicular from squark family mixings in generic supersymmetric models. Estimates of the upper bounds on Pμperpendicular are also given. It is found that a supersymmetry-induced right-handed quark current from W boson exchange gives an upper limit on Pμperpendicular as large as a few percent, whereas, with a charged-Higgs-boson-exchange induced pseudoscalar interaction, Pμperpendicular is no larger than a few tenths of a percent. Possible correlations between the muon polarization measurements in K+→μ+νγ and K+→π0μ+ν decays are discussed, and distinctive patterns of this correlation from squark family mixings and from the three-Higgs-doublet model are noted. copyright 1997 The American Physical Society