Flavor-Nonconservation and CP-Violation with Singlet Quarks

Some aspects are considered on the flavor-nonconservation and $CP$-violation arising from the quark mixings with singlet quarks. In certain models incorporating the singlet quarks, the contributions of the quark couplings to the neutral Higgs fields may become more significant than those of the neutral gauge interactions. Then, they would provide distinct signatures for new physics beyond the standard model in various flavor-nonconserving and $CP$-violating processes such as the neutron electric dipole moment, $D^0$-${\bar{D}}^0$, $K^0$-${\bar{K}}^0$, $B^0$-${\bar{B}}^0$, $b\to s\gamma$, and so on.