10,990 research outputs found

    Natural Dirac Neutrinos from Warped Extra Dimension

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    Dirac neutrinos arising from gauged discrete symmetry \`a la Krauss-Wilczek are implemented in the minimal custodial Randall-Sundrum model. In the case of a normal hierarchy, all lepton masses and mixing pattern can be naturally reproduced at the TeV scale set by the electroweak constraints, while simultanously satisfy bounds from lepton flavour violation. A nonzero neutrino mixing angle, θ13\theta_{13}, is generic in the scenario, as well as the existence of sub-TeV right-handed Kaluza-Klein neutrinos, which may be searched for at the LHC.Comment: Talk given at the 2nd Young Researchers Workshop "Physics Challenges in the LHC Era", Frascati, May 10 and 13, 2010, 6 page

    U(1)BLU(1)_{B-L} extra-natural inflation with Standard Model on a brane

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    The interrelation between inflationary cosmology and new physics beyond the Standard Model (SM) is studied in a U(1)BLU(1)_{B-L} extension of the SM embedded in a (4+1)-dimensional spacetime. In the scenario we study, the inflaton arises from the Wilson loop of the U(1)BLU(1)_{B-L} gauge group winding an extra-dimensional cycle. Particular attention is paid to the coupling between the inflaton and SM particles that are confined on a brane localised in the extra dimension. We find that the inflaton decay channels are rather restricted in this scenario and the resulting reheating temperature is relatively low.Comment: 1+14 page

    Phenomenology from a U(1) gauged hidden sector

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    We consider the phenomenological consequences of a hidden Higgs sector extending the Standard Model (SM), in which the matter content are uncharged under the SM gauge groups. We consider a simple case where the hidden sector is gauged under a U(1) with one Higgs singlet. The only couplings between SM and the hidden sector are through mixings between the neutral gauge bosons of the two respective sectors, and between the Higgs bosons. We find signals testable at the LHC that can reveal the existence and shed light on the nature of such a hidden sector.Comment: 5 pages, 2 figures. Talk given at the Lake Louise Winter Institute 2007, Feb. 19-24, Alberta, Canad

    Testing Realistic Quark Mass Matrices in the Custodial Randall-Sundrum Model with Flavor Changing Top Decays

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    We study quark mass matrices in the Randall-Sundrum (RS) model with bulk symmetry SU(2)L×SU(2)R×U(1)BLSU(2)_L \times SU(2)_R \times U(1)_{B-L}. The Yukawa couplings are assumed to be within an order of magnitude of each other, and perturbative. We find that quark mass matrices of the symmetrical form proposed by Koide \textit{et. al.} [Y. Koide, H. Nishiura, K. Matsuda, T. Kikuchi and T. Fukuyama, Phys. Rev. D {\bf 66}, 093006 (2002)] can be accommodated in the RS framework with the assumption of hierarchyless Yukawa couplings, but not the hermitian Fritzsch-type mass matrices. General asymmetrical mass matrices are also found which fit well simultaneously with the quark masses and the Cabibbo-Kobayashi-Maskawa matrix. Both left-handed (LH) and right-handed (RH) quark rotation matrices are obtained that allow analysis of flavour changing decay of both LH and RH top quarks. At a warped down scale of 1.65 TeV, the total branching ratio of t \ra Z + jets can be as high as 5×106\sim 5 \times 10^{-6} for symmetrical mass matrices and 2×105\sim 2 \times 10^{-5} for asymmetrical ones. This level of signal is within reach of the LHC.Comment: 30 pages, 6 figures. Reference added, typos corrected, discussions in Sec. IV B expanded. Version conforms to the published versio

    A Very Narrow Shadow Extra Z-boson at Colliders

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    We consider the phenomenological consequences of a hidden Higgs sector extending the Standard Model (SM), in which the ``shadow Higgs'' are uncharged under the SM gauge groups. We consider a simple U(1) model with one Higgs singlet. One mechanism which sheds light on the shadow sector is the mixing between the neutral gauge boson of the SM and the additional U(1) gauge group. The mixing happens through the usual mass-mixing and also kinetic-mixing, and is the only way the ``shadow ZZ'' couples to the SM. We study in detail modifications to the electroweak precision tests (EWPTs) that the presence of such a shadow sector would bring, which in turn provide constraints on the kinetic-mixing parameter, sϵs_\epsilon, left free in our model. The shadow ZZ production rate at the LHC and ILC depends on sϵs_\epsilon. We find that observable event rate at both facilities is possible for a reasonable range of sϵs_\epsilon allowed by EWPTs.Comment: 10 pages, 7 figures. Note and refs. adde

    Twisted Mass Finite Volume Effects

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    We calculate finite volume effects on the pion masses and decay constant in twisted mass lattice QCD (tmLQCD) at finite lattice spacing. We show that the lighter neutral pion in tmLQCD gives rise to finite volume effects that are exponentially enhanced when compared to those arising from the heavier charged pions. We demonstrate that the recent two flavour twisted mass lattice data can be better fitted when twisted mass effects in finite volume corrections are taken into account.Comment: 17 pages, revte

    Strange quarks in quenched twisted mass lattice QCD

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    Two twisted doublets, one containing the up and down quarks and the other containing the strange quark with an SU(2)-flavor partner, are used for studies in the meson sector. The relevant chiral perturbation theory is presented, and quenched QCD simulations (where the partner of the strange quark is not active) are performed. Pseudoscalar meson masses and decay constants are computed; the vector and scalar mesons are also discussed. A comparison is made to the case of an untwisted strange quark, and some effects due to quenching, discretization, and the definition of maximal twist are explored.Comment: 37 pages, 12 figures, accepted for publicatio