Flavor nonconservation and CP violation from quark mixings with singlet quarks

Flavor nonconserving and CP violating effects of the quark mixings are investigated in electroweak models incorporating singlet quarks. Especially, the D0–D̄0 mixing and the neutron electric dipole moment, which are mediated by the up-type quark couplings to the neutral Higgs fields, are examined in detail for reasonable ranges of the quark mixings and the singlet Higgs mass scale. These neutral Higgs contributions are found to be comparable to or smaller than the experimental bounds even for the case where the singlet Higgs mass scale is of the order of the electroweak scale and a significant mixing is present between the top quark and the singlet quarks.