Flavor mixing

Recently, some researchers have been talking about the so-called 'fifth force'. This name suggests that four forces are already known to exist, which are generally called the strong, electromagnetic, weak, and gravitational interactions. However, the standard model of particle physics tells a different story; they are the gauge interactions, Yukawa interactions, Higgs interactions, and gravity. Of the first three, only the gauge interactions have been verified experimentally. However, the other two are truly necessary ingredients of the standard model to make it work. The present report discusses such matters as Kobayashi-Maskawa matrix, KM matrix elements, CP violation, particle antiparticle mixing, flavor-charging neutral current decays, generation crossover, FCNC decay, and lepton flavor mixing. It is concluded that the Kobayashi-Maskawa scheme for the quark mixing is in good shape. So far five out of nine matrix elements are experimentally determined. Nonzero value of the sixth matrix element Kub is essential for the KM scenario of CP violation. The observed large B-B-bar mixing suggests a heavy top quark. A lot of work is still needed towards the understanding of 'flavor'. (N.K.)