2,527 research outputs found

    A holographic composite Higgs model

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    If the Higgs boson has a composite nature, it might be the 4-dimensional hologram of a gauge field living in a warped extra dimension. In this talk I discuss a minimal, calculable model that passes all electroweak precision tests, included that from Z->bb, and gives a natural account of the electroweak symmetry breaking.Comment: 4 pages, talk given at IFAE 2006, Pavia, Italy, April 19-21 200

    New Physics at the LHC: Strong vs Weak symmetry breaking

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    What kind of New Physics, if any, we expect to discover at the LHC? I will try to address this formidable question by re-formulating it as follows: is the breaking of the electroweak symmetry strong or weak ?Comment: Talk given at IFAE 2009, Bari, Italy, 15-17 April 200

    The Supersymmetric Flavor Problem for Heavy First-Two Generation Scalars at Next-to-Leading Order

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    We analyze in detail the constraints on SUSY-model parameters obtained from K-Kbar mixing in the hypothesis of a splitted SUSY spectrum. FCNC contributions from gluino-squark-quark interactions are studied in the so-called mass insertion approximation. We present boundaries on mass insertions and on SUSY mass scales. We improve previous results by including the NLO-QCD corrections to Delta S=2 effective Hamiltonian and the complete set of B-parameters for the evaluation of hadronic matrix elements. A full set of magic-numbers, that can be used for further analyses of these models, is also given. We find that the inclusion of NLO-QCD corrections and the B-parameters change the results obtained at LO and in the Vacuum Insertion Approximation by an amount of about 25-35%.Comment: 22 Latex pages, 5 figures; Figs. 1,2 redrawn for K=0.22, section 4.1 revisited, references corrected. Submitted to European Journal of Physics

    Dispersion Relations for Electroweak Observables in Composite Higgs Models

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    We derive dispersion relations for the electroweak oblique observables measured at LEP in the context of SO(5)/SO(4)SO(5)/SO(4) composite Higgs models. It is shown how these relations can be used and must be modified when modeling the spectral functions through a low-energy effective description of the strong dynamics. The dispersion relation for the parameter ϔ3\epsilon_3 is then used to estimate the contribution from spin-1 resonances at the 1-loop level. Finally, it is shown that the sign of the contribution to the S^\hat S parameter from the lowest-lying spin-1 states is not necessarily positive definite, but depends on the energy scale at which the asymptotic behavior of current correlators is attained.Comment: 34 pages, 4 figures. v2: a few minor changes, typos corrected, list of references revise

    One-loop effects from spin-1 resonances in Composite Higgs models

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    We compute the 1-loop correction to the electroweak observables from spin-1 resonances in SO(5)/SO(4) composite Higgs models. The strong dynamics is modeled with an effective description comprising the Nambu-Goldstone bosons and the lowest-lying spin-1 resonances. A classification is performed of the relevant operators including custodially-breaking effects from the gauging of hypercharge. The 1-loop contribution of the resonances is extracted in a diagrammatic approach by matching to the low-energy theory of Nambu-Goldstone bosons. We find that the correction is numerically important in a significant fraction of the parameter space and tends to weaken the bounds providing a negative shift to the S parameter.Comment: 45 pages, 13 figures. v2: minor corrections, conclusions unchanged. v3: two diagrams in Fig.13 correctly redraw

    A brief introduction to the model microswimmer {\it Chlamydomonas reinhardtii}

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    The unicellular biflagellate green alga {\it Chlamydomonas reinhardtii} has been an important model system in biology for decades, and in recent years it has started to attract growing attention also within the biophysics community. Here we provide a concise review of some of the aspects of {\it Chlamydomonas} biology and biophysics most immediately relevant to physicists that might be interested in starting to work with this versatile microorganism.Comment: 16 pages, 7 figures. To be published as part of EPJ S

    Top Compositeness and Precision Unification

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    The evolution of Standard Model gauge couplings is studied in a non-supersymmetric scenario in which the hierarchy problem is resolved by Higgs compositeness above the weak scale. It is argued that massiveness of the top quark combined with precision tests of the bottom quark imply that the right-handed top must also be composite. If, further, the Standard Model gauge symmetry is embedded into a simple subgroup of the unbroken composite-sector flavor symmetry, then precision coupling unification is shown to occur at~10^{15} GeV, to a degree comparable to supersymmetric unification.Comment: v2: few extra comments added; slightly shorter version published in PR

    Phenomenology of a light scalar: the dilaton

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    We make use of the language of non-linear realizations to analyze electro-weak symmetry breaking scenarios in which a light dilaton emerges from the breaking of a nearly conformal strong dynamics, and compare the phenomenology of the dilaton to that of the well motivated light composite Higgs scenario. We argue that -- in addition to departures in the decay/production rates into massless gauge bosons mediated by the conformal anomaly -- characterizing features of the light dilaton scenario (as well as other scenarios admitting a light CP-even scalar not directly related to the breaking of the electro-weak symmetry) are off-shell events at high invariant mass involving two longitudinally polarized vector bosons and a dilaton, and tree-level flavor violating processes. Accommodating both electro-weak precision measurements and flavor constraints appears especially challenging in the ambiguous scenario in which the Higgs and the dilaton fields strongly mix. We show that warped higgsless models of electro-weak symmetry breaking are explicit and tractable realizations of this limiting case. The relation between the naive radion profile often adopted in the study of holographic realizations of the light dilaton scenario and the actual dynamical dilaton field is clarified in the Appendix.Comment: 21 page

    Higgs pair production in vector-boson fusion at the LHC and beyond

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    The production of pairs of Higgs bosons at hadron colliders provides unique information on the Higgs sector and on the mechanism underlying electroweak symmetry breaking (EWSB). Most studies have concentrated on the gluon fusion production mode which has the largest cross section. However, despite its small production rate, the vector-boson fusion channel can also be relevant since even small modifications of the Higgs couplings to vector bosons induce a striking increase of the cross section as a function of the invariant mass of the Higgs boson pair. In this work, we exploit this unique signature to propose a strategy to extract the hhVVhhVV quartic coupling and provide model-independent constraints on theories where EWSB is driven by new strong interactions. We take advantage of the higher signal yield of the bbˉbbˉb\bar b b\bar b final state and make extensive use of jet substructure techniques to reconstruct signal events with a boosted topology, characteristic of large partonic energies, where each Higgs boson decays to a single collimated jet . Our results demonstrate that the hhVVhhVV coupling can be measured with 45% (20%) precision at the LHC for L=\mathcal{L}= 300 (3000) fb−1^{-1}, while a 1% precision can be achieved at a 100 TeV collider.Comment: Updated to match published version in EPJC and fixed typo in Tab. 10 (column labels a & b were swapped