CP violation in semileptonic tau lepton decays

The leading order contribution to the direct CP asymmetry in τ^±→K^±π⁰ν_τ decay rates is evaluated within the standard model. The weak phase required for CP violation is introduced through an interesting mechanism involving second order weak interactions, which is also responsible for tiny violations of the ΔS=ΔQ rule in K_l3 decays. The calculated CP asymmetry turns out to be of order 10^-12, leaving a large window for studying effects of nonstandard sources of CP violation in this observable.