282 research outputs found
Schwinger-Dyson approach and its application to generate a light composite scalar
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
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
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
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
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
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
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
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