TestingCPinKμ3decays

K factories will open the way for high-precision CP tests in $K_{\mu 3}$ decays. The standard model does not predict CP breaking in this process. We consider here the effects of nonstandard interactions mediated by vector and scalar particles and by leptoquarks. We show that, for the only experimentally measurable quantity, vector particles alone never induce CP violation, and give a general expression for the CP breaking induced by scalars and leptoquarks.