138 research outputs found

    Gauge bosons in a five-dimensional theory with localized gravity

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    We consider the possibility of gauge bosons living in the recently proposed five-dimensional theory with localized gravity. We study the mass spectrum of the Kaluza-Klein (KK) excitations of the gauge fields and calculate their couplings to the boundaries of the fifth dimension. We find a different behaviour from the case of the graviton. In particular, we find that the massless mode is not localized in the extra dimension and that the KK excitations have sizeable couplings to the two boundaries. We also discuss possible phenomenological implications for the case of the standard model gauge bosons.Comment: 10 pages, Late

    Top Quark Compositeness: Feasibility and Implications

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    In models of electroweak symmetry breaking in which the SM fermions get their masses by mixing with composite states, it is natural to expect the top quark to show properties of compositeness. We study the phenomenological viability of having a mostly composite top. The strongest constraints are shown to mainly come from one-loop contributions to the T-parameter. Nevertheless, the presence of light custodial partners weakens these bounds, allowing in certain cases for a high degree of top compositeness. We find regions in the parameter space in which the T-parameter receives moderate positive contributions, favoring the electroweak fit of this type of models. We also study the implications of having a composite top at the LHC, focusing on the process pp-> t\bar t t\bar t (b\bar b) whose cross-section is enhanced at high-energies.Comment: 26 pages, 11 figure

    Flavor hierarchies from dynamical scales

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    One main obstacle for any beyond the SM (BSM) scenario solving the hierarchy problem is its potentially large contributions to electric dipole moments. An elegant way to avoid this problem is to have the light SM fermions couple to the BSM sector only through bilinears, fˉf\bar ff. This possibility can be neatly implemented in composite Higgs models. We study the implications of dynamically generating the fermion Yukawa couplings at different scales, relating larger scales to lighter SM fermions. We show that all flavor and CP-violating constraints can be easily accommodated for a BSM scale of few TeV, without requiring any extra symmetry. Contributions to B physics are mainly mediated by the top, giving a predictive pattern of deviations in ΔF=2\Delta F=2 and ΔF=1\Delta F=1 flavor observables that could be seen in future experiments.Comment: 25 pages, 5 figures; v2: corrections in some estimate

    Towards the Ultimate SM Fit to Close in on Higgs Physics

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    With the discovery of the Higgs at the LHC, experiments have finally addressed all aspects of the Standard Model (SM). At this stage, it is important to understand which windows for beyond the SM (BSM) physics are still open, and which are instead tightly closed. We address this question by parametrizing BSM effects with dimension-six operators and performing a global fit to the SM. We separate operators into different groups constrained at different levels, and provide independent bounds on their Wilson coefficients taking into account only the relevant experiments. Our analysis allows to assert in a model-independent way where BSM effects can appear in Higgs physics. In particular, we show that deviations from the SM in the differential distributions of h->Vff are related to other observables, such as triple gauge-boson couplings, and are then already constrained by present data. On the contrary, BR(h-> Z+gamma) can still hide large deviations from the SM.Comment: 20 pages, 5 figures, v2: typos corrected. JHEP versio

    Baryon Physics in Holographic QCD

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    In a simple holographic model for QCD in which the Chern-Simons term is incorporated to take into account the QCD chiral anomaly, we show that baryons arise as stable solitons which are the 5D analogs of 4D skyrmions. Contrary to 4D skyrmions and previously considered holographic scenarios, these solitons have sizes larger than the inverse cut-off of the model, and therefore they are predictable within our effective field theory approach. We perform a numerical determination of several static properties of the nucleons and find a satisfactory agreement with data. We also calculate the amplitudes of ``anomalous'' processes induced by the Chern-Simons term in the meson sector, such as omega -> pi gamma and omega -> 3pi. A combined fit to baryonic and mesonic observables leads to an agreement with experiments within 16%.Comment: 18 pages, version to appear in Nucl. Phys.

    The Composite Higgs and Light Resonance Connection

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    Weinberg sum-rules have been used in the past to successfully predict the electromagnetic contribution to the charged-pion mass as a function of the meson masses. Following the same approach we calculate in the minimal composite Higgs model (MCHM) the Higgs mass as a function of the fermionic resonance masses. The simplicity of the method allows us to study several versions of the MCHM and show that a Higgs with a mass around 125 GeV requires, quite generically, fermionic resonances below the TeV, and therefore accessible at the LHC. We also examine the couplings of the Higgs to the SM fermions and calculate their deviation from the SM value.Comment: Version to be published in JHE

    Baryon physics in a five-dimensional model of hadrons

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    We review the procedure to calculate baryonic properties using a recently proposed five-dimensional approach to QCD. We show that this method give predictions to baryon observables that agree reasonable well with the experimental data.Comment: Contribution to "The Multi-facet of Skyrmions" edited by G. Brown and M. Rho for World Scientific Publishing Co, 30
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