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Dirac Neutrinos, Leptogenesis and a Vaniching Higgs @ LHC

Thomas Underwood (University of Durham)
06 July 2007, 11:15 - 13:00

We consider a minimal lepton number conserving extension to the Standard Model providing Dirac neutrinos without resorting to tiny Yukawa couplings. Small neutrino masses arise because the model contains a spontaneously broken global U(1) symmetry in its gauge singlet (or `phantom) sector - this suppresses neutrino masses via a Froggatt-Nielsen type mechanism. We show that successful baryogenesis through leptogenesis is possible in this case and that this suggests an electroweak scale VEV for the gauge singlet scalar. The model contains two physical Higgs bosons and a massless Goldstone boson. The existence of the Goldstone boson suppresses the Higgs to bb(bar) branching ratio and instead Higgs bosons will decay mainly into invisible Goldstone and/or to vector boson pairs. We have studied the implications of this scenario for Higgs discovery at the LHC.
Underwood_T.pdf [3264 KBytes]