230 research outputs found

    Signatures of Non-Standard Electroweak Symmetry Breaking

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    This is the write-up of a talk given at the EW session in Moriond (March 2012). I summarize some non-standard electroweak scenarios, and how they predict the existence of new spin-two resonances. Spin-two resonances, whether coming from the compactification of extra-dimensions or from a new sector of strong interactions, exhibit the same interactions with the Standard Model. This is a consequence of Lorentz and CP invariance, which we assume would be preserved by the new strong sector. Although this would seem to support the holographic duality between strongly interacting theories in four-dimensions and extra-dimensional theories, I show that there is a way to distinguish between the two sides of the "duality", which constitutes an explicit example of its breakdown

    (Not) Summing over Kaluza-Kleins

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    Models in extra-dimensions have unique features. Many of their surprising properties simply result from the underlying 5D structure. This structure shows up as ``Sum Rules'' involving the whole tower of Kaluza-Kleins. In this paper, we present a holographic shortcut and derive these results without solving the eigenvalue problem: we express 4D physical quantities directly in terms of the 5D metric. In warped space, one can go further and isolate the effect of the new physics sector. This method can be used for any 5D model, and we apply it here to the case of holographic QCD and technicolor

    Non standard neutrino interactions at LEP2 and the LHC

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    We consider Non-Standard neutrino Interactions (NSI) connecting two neutrinos with two first-generation fermions (e,ue, u or dd), which we assume to arise at at dimension eight due to New Physics. The coefficient is normalised as 4ϵGF/24 \epsilon G_F/\sqrt{2}. We explore signatures of NSI-on-electrons at LEP2, and of NSI-on-quarks at the LHC, treating the NSI as contact interactions at both energies. In models where the coefficients of dangerous dimension six operators are suppressed by cancellations, LEP2 provides interesting bounds on NSI operators (\epsilon \lsim 10^{-2} - 10^{-3}), which arise because s200\sqrt{s} \sim 200 GeV, and the cancellation applied at zero momentum transfer. At the LHC, we use the Equivalence Theorem, which relates the longitudinal WW to the Higgs, to estimate the rate for qˉqW+Weα+eβ\bar{q} q W^+W^- e_\alpha^+ e_\beta^- induced by NSI. We find that the cross-section is small, but that the outgoing particles have very high pT>400p_T > 400 GeV, which reduces the issue of backgrounds. In a conservative scenario, we find that the LHC at 14 TeV and with 100 fb1^{-1} of data would have a sensitivity to \epsilon \gsim 3 \times 10^{-3}.Comment: 4 pages, contribution to NUFACT 11, XIIIth International Workshop on Neutrino Factories, Super beams and Beta beams, 1-6 August 2011, CERN and University of Geneva (Submitted to IOP conference series

    Prima Facie Evidence against Spin-Two Higgs Impostors

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    The new particle X recently discovered by the ATLAS and CMS Collaborations is widely expected to have spin zero, but this remains to be determined. The leading alternative is that X has spin two, presumably with graviton-like couplings. We show that measurements of the X particle to pairs of vector bosons constrain such scenarios. In particular, a graviton-like Higgs impostor in scenarios with a warped extra dimension of AdS type is prima facie excluded, principally because they predict too small a ratio between the X couplings to WW and ZZ, compared with that to photons. The data also disfavour universal couplings to pairs of photons and gluons, which would be predicted in a large class of graviton-like models.Comment: 17 pages, 3 figure

    Associated Production Evidence against Higgs Impostors and Anomalous Couplings

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    There is still no proof that the new particle XX recently discovered by the ATLAS and CMS Collaborations indeed has spin zero and positive parity, as confidently expected. We show here that the energy dependence of associated W/Z+XW/Z + X production would be much less for a JP=0+J^P = 0^+ boson with minimal couplings, such as the Higgs boson of the Standard Model, than for a spin-two particle with graviton-like couplings or a spin-zero boson with non-minimal couplings. The W/Z+(Xbˉb)W/Z + (X \to {\bar b}b) signal apparently observed by the CDF and D0 Collaborations can be used to predict the cross section for the same signal at the LHC that should be measured under the spin-two and different spin-zero hypotheses. The spin-two prediction exceeds by an order of magnitude the upper limits established by the ATLAS and CMS Collaborations, which are consistent with the minimal 0+0^+ prediction, thereby providing {\it secunda facie} evidence against spin-two Higgs impostors. Similar analyses of energy dependences provide evidence against 00^- impostors, non-minimal scalar boson couplings, including the best LHC limits on dimension-six operators. Comparing the LHC vector boson fusion cross sections at 7 and 8 TeV in the centre of mass provides additional but weaker evidence in favour of the identification of the XX particle as a JP=0+J^P = 0^+ boson with minimal couplings.Comment: 15 pages, 7 figure
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