CP violation in the Cabbibo-suppressed decay τ→Kπντ with polarized τ leptons

CP violation from physics beyond the Standard Model (SM) is investigated in the Cabbibo-suppressed decay τ→Kπντ with polarized τ leptons, to which both the JP=1− resonance K∗ and the JP=0+ resonance K∗0 contribute. In addition to the CP-odd rate asymmetry, τ polarization enables us to construct three additional CP-odd polarization asymmetries that can be enhanced due to the interference between the K∗ and K∗0, and whose magnitudes depend crucially on the K∗0 decay constant, fK∗0. Taking a QCD sum rule estimate of fK∗0=45 MeV and the present experimental constraints on the CP-odd parameters into account, we estimate quantitatively the maximally-allowed values for the CP-odd rate and polarization asymmetries in the multi-Higgs-doublet (MHD) model and the scalar-leptoquark (SLQ) models consistent with the SM gauge symmetry where neutrinos are massless and left-handed as in the SM. We find that the CP-odd rate and polarization asymmetries are of a similar size for highly-polarized τ leptons and, for their maximally-allowed values, CP violation in the MHD model and two SLQ models may be detected with about 106 and 107 τʹs at the 1σ level.