Flavor and CP Violation Induced by Atmospheric Neutrino Mixing

After discovery of the atmospheric neutrino oscillation by the superKamiokande experiment in 98’ [1], it is found that the lepton sector has much different flavor structure from the quark sector [2][3]. The seesaw mechanism is the most promising model to explain the tiny neutrino masses and the neutrino oscillation [4]. However, the observed mixing angles between the first and second and between second and third generations are almost maximal, and those are different from the naive expectation in the extension of the seesaw mechanism to the grand unified theories (GUTs). Various attempts to understand those mismatches between quark and lepton mixing angles have been made so far. We may find new clues to understand the origin of the neutrino masses in the future precision experiments of hadrons and leptons. In the supersymmetric (SUSY) models, the flavorand CP-violating phenomena in hadron and lepton physics are windows to probe flavor structure in the high energy physics, such as the seesaw mechanism and the GUTs. The imprints may be generated in the SUSY-breaking slepton or squark mass terms if the SUSY-breaking terms are generated at the higher than the energy scale. In this case the SUSY-breaking terms induce the sizable effect to the flavorand CP-violating processes in hadrons and leptons, since they are suppressed by only the SUSY-breaking scale, not the energy scale responsible to the flavor violation such as the right-handed neutrino mass or GUT scale [5]. In the SUSY seesaw mechanism the radiative correction by the neutrino Yukawa coupling induces the left-handed slepton mixing even if the soft SUSY-breaking terms are universal at the GUT or Planck scale. This lepton-flavor violation (LFV) leads to the radiative LFV decay of tau and muon [6]. If the SUSY seesaw model is extended to the SUSY GUTs, the right-handed down-type squarks also have the flavor-violating SUSY-breaking mass terms since they are embedded in common SU(5) multiplets with the lefthanded leptons [7][8]. This may lead to new flavorand CP-violating source. The Belle and BaBar experiments in the KEK and SLAC B factories, give new information about the flavor violation of the third generations. The CKM dominance in the flavorand CP-violating hadron phenomena is almost confirmed by the experiments. However, the Belle experiment reports that the CP asymmetry in Bd → φKs is 3.5σ deviated from the StandardModel (SM) prediction [9]. At present the BaBar experiment does not observe such a large deviation, and the combined result is not yet significant [10]. However, the Belle’s result might be a signature of the new physics. In addition to them, the experiments are improving bounds on the LFV tau decay modes by about one order of magnitude [11]. Now the physics in high luminosity B factories, whose integrate luminosities may reach to the order of ab, is discussed. If these super B factories are constructed, we may get new information about the origin of the neutrino masses. In this article, we review the third generation