Splitting Triplet and Doublet in Extra Dimensions

A novel mechanism to realize the triplet-doublet splitting in supersymmetric SU(5) grand unified theories is proposed in the framework of higher dimensional theories where chiral multiplets are localized due to kink configuration of a SU(5) singlet. An adjoint Higgs field which spontaneously breaks the SU(5) gauge symmetry is assumed to be involved with the localization process, splitting the wave functions of the color-triplet Higgs from its doublet counterpart. The resulting effective four-dimensional theory does not possess manifest SU(5) invariance. By adjusting couplings, the doublet mass can be exponentially suppressed. We also show that dimension 5 proton decay from triplet Higgs exchange can be suppressed to a negligible level.Comment: 9 pages, 2 figures, some references adde

Relic abundance of dark matter in the minimal universal extra dimension model

We investigate the relic abundance of dark matter in the minimal universal extra dimension model including resonance processes by second Kaluza-Klein (KK) particles in all coannihilation processes. After including second KK resonance processes, the relic abundance of dark matter is reduced by about 30%. Thus, the compactification scale 1/R of the extra dimension consistent with the WMAP observation is increased by a few hundred GeV. As a result, the cosmologically allowed compactification scale is 600 GeV < 1/R < 1400 GeV for Lambda R = 20.Comment: 24 pages, 7 figure

Lepton flavor violation in the triplet Higgs model

The triplet Higgs model, which is an extension of the standard model with a weak-scale triplet Higgs boson, is capable of generating small neutrino masses naturally. We investigate lepton flavor violation mediated by the triplet Higgs boson. We stress that various neutrino mass patterns could be distinguished by measuring the lepton flavor violating processes. \mu \to eee decay is significantly enhanced in the case of the degenerate masses or the inverted-hierarchical masses compared with that in the case of the hierarchical masses. On the other hand, the \mu \to e \gamma rate and the \mu - e conversion ratio in nuclei is almost insensitive to the mass spectra. We also emphasize that these decay rates tend to increase as the magnitude of U_{e3} increases. Lepton flavor nonconserving \tau decay modes are expected to be unobservable at planned experiments in the light of the current upper bounds of flavor violating muonic decay.Comment: 11 pages, 3 figures, typos correcte