282 research outputs found

    Schwinger-Dyson approach and its application to generate a light composite scalar

    Full text link
    We discuss the possibility of generating a light composite scalar boson, in a scenario that we may generically call Technicolor, or in any variation of a strongly interacting theory, where by light we mean a scalar composite mass about one order of magnitude below the characteristic scale of the strong theory. Instead of most of the studies about a composite Higgs boson, which are based on effective Lagrangians, we consider this problem in the framework of non-perturbative solutions of the fermionic Schwinger-Dyson and Bethe-Salpeter equations. We study a range of mechanisms proposed during the recent years to form such light composite boson, and verify that such possibility seems to be necessarily associated to a fermionic self-energy that decreases slowly with the momentum.Comment: 35 pages, 6 figures, few typos corrected. Version to appear in IJMP

    Scalar bosons in Minimal and Ultraminimal Technicolor: Masses, trilinear couplings and widths

    Full text link
    We compute masses, trilinear self-couplings and decay widths into weak bosons of the scalar composite bosons in the case of the Minimal and Ultraminimal technicolor models. The masses, computed via the Bethe-Salpeter equation, turn out to be light and the trilinear couplings smaller than the one that would be expected when compared to a fundamental Standard Model scalar boson with the same mass. The decay widths into electroweak bosons of the Ultraminimal model scalars bosons are much smaller than the one of the Minimal model.Comment: 15 pages, 1 figure, improved discussion, new references and typos corrected, matchs version to be publishe

    Deciphering the minimum of energy of some walking technicolor models

    Full text link
    There are quasi-conformal theories, like the Minimal and Ultraminimal Technicolor models, which may break dynamically the gauge symmetry of the Standard Model and at the same time are compatible with electroweak precision data. The main characteristic of this type of models is their fermionic content in one or more higher dimensional representations, therefore it is not immediate to know which model leads to the most attractive channel or the minimum vacuum energy state. We discuss the effective potential for composite operators for these models, verifying that their vacuum energy values are different, with the Ultraminimal model having a deeper minimum of energy.Comment: 4 pages, 2 figures, published version

    A dynamical mechanism to explain the top-bottom quark mass hierarchy

    Full text link
    We discuss the mass splitting between the the top and bottom quarks in a technicolor scenario. The model proposed here contains a left-right electroweak gauge group. An extended technicolor group and mirror fermions are introduced. The top-bottom quark mass splitting turns out to be intimately connected to the breaking of the left-right gauge symmetry. Weak isospin violation occurs within the experimental limits.Comment: Changes are made in sections I, II and IV; an new figure added; results unchanged; accepted for publication in Int. J. Mod. Phys.

    Energy criterion to select the behavior of dynamical masses in technicolor models

    Full text link
    We propose a quite general ansatz for the dynamical mass in technicolor models. We impose on this ansatz the condition for formation of the tightest composite boson state, or the criterion that it should lead to the deepest minimum of energy. This criterion indicates a particular form of the technifermion self energy.Comment: 4 pages, 3 figures; to appear in Phys. Lett.

    Schwinger-Dyson equation boundary conditions induced by ETC radiative corrections

    Full text link
    The technicolor (TC) Schwinger-Dyson equations (SDE) should include radiative corrections induced by extended technicolor (ETC) interactions when TC is embedded into a larger theory including also QCD. These radiative corrections couple the different strongly interacting Dyson equations. We discuss how the boundary conditions of the coupled SDE system are modified by these corrections, and verify that the ultraviolet behavior of the self-energies are described by a function that decreases logarithmically with momentum.Comment: 15 pages, 2 figure

    A 125 GeV Scalar Boson and SU(N_{TC})\otimes SU(3)_{{}_{L}}\otimes U(1)_{{}_{X}} models

    Full text link
    We verify that SU(N)_{{}_{TC}}\otimes SU(3)_{{}_{L}}\otimes U(1)_{{}_{X}} models, where the gauge symmetry breaking is totally dynamical and promoted by the non-Abelian technicolor (TC) group and the strong Abelian interactions, are quite constrained by the LHC data. The theory contains a T quark self-energy involving the mixing between the neutral gauge bosons, which introduces the coupling between the light and heavy composite scalar bosons of the model. We determine the lightest scalar boson mass for these models from an effective action for composite operators, assuming details about the dynamics of the strong interaction theories. Comparing the value of this mass with the ATLAS and CMS observation of a new boson with a mass M_{\phi} \sim 125GeV and considering the lower bound determined by the LHC Collaborations on the heavy neutral gauge boson (Z^\prime) present in these models, we can establish constraints on the possible models. For example, if SU(N)_{{}_{TC}}\equiv SU(2)_{{}_{TC}}, with technifermions in the fundamental representation, the model barely survives the confrontation with the LHC data.Comment: 19 pages, 3 figure
    corecore