Neutrino masses, muon g-2, and lepton-flavour violation in the supersymmetric see-saw model

Abstract

In the light of the recent muon (g_mu-2) result by the E821 experiment at the Brookhaven National Laboratory, we study the event rates of the charged lepton-flavour-violating (LFV) processes in the supersymmetric standard model (SUSY SM) with the heavy right-handed neutrinos (SUSY see-saw model). Since the left-handed sleptons get the LFV masses via the neutrino Yukawa interaction in this model, the event rate of mu->e gamma and the SUSY-SM correction to (g_mu-2)/2 (δa_mu^{SUSY}) are strongly correlated. When the left-handed sleptons have a LFV mass between the first and second generations ((m^2_L)_{12}) in the mass matrix, it should be suppressed by \sim 10^{-3} ({10^-9}/δa_mu^{SUSY}) compared with the diagonal components (m_{SUSY}^2), from the current experimental bound on mu-> e gamma. The recent (g_mu-2) result indicates {δa_mu^{SUSY}}\sim 10^{-9}. The future charged LFV experiments could cover (m^2_L)_{12}/m_{SUSY}^2\gsim 10^{-(5-6)}. These experiments will give a significant impact on the flavour models and the SUSY-breaking models. In the SUSY see-saw model (m^2_L)_{12} is proportional to square of the tau-neutrino Yukawa-coupling constant. In the typical models where the neutrino-oscillation results are explained and the top-quark and tau-neutrino Yukawa couplings are unified at the GUT scale, a large LFV mass of (m^2_L)_{12}/m_{SUSY}^2\gsim 10^{-4} is generated, and the large LFV event rates are predicted. We impose a so-called no-scale condition for the SUSY-breaking parameters at the GUT scale, which suppresses the FCNC processes, and derive the conservative lower bound on mu-> egamma. The predicted Br(mu-> e gamma) could be covered at the future LFV experiments.