545 research outputs found
Higgsless Models: Lessons from Deconstruction
This talk reviews recent progress in Higgsless models of electroweak symmetry
breaking, and summarizes relevant points of model-building and phenomenology.Comment: 12 pages, 2 figures, Presented at the X Mexican Workshop on Particles
and Field
Oblique Corrections in Deconstructed Higgsless Models
In this talk, using deconstruction, we analyze the form of the corrections to
the electroweak interactions in a large class of ``Higgsless'' models of
electroweak symmetry breaking, allowing for arbitrary 5-D geometry,
position-dependent gauge coupling, and brane kinetic energy terms. Many models
considered in the literature, including those most likely to be
phenomenologically viable, are in this class. By analyzing the asymptotic
behavior of the correlation function of gauge currents at high momentum, we
extract the exact form of the relevant correlation functions at tree-level and
compute the corrections to precision electroweak observables in terms of the
spectrum of heavy vector bosons. We determine when nonoblique corrections due
to the interactions of fermions with the heavy vector bosons become important,
and specify the form such interactions can take. In particular we find that in
this class of models, so long as the theory remains unitary, S - 4 c^2_W T >
O(1), where S and T are the usual oblique parameters.Comment: 4 pages, 1 figure, to appear in the proceedings of SUSY 2004 : The
12th International Conference on Supersymmetry and Unification of Fundamental
Interactions, held at Epochal Tsukuba, Tsukuba, Japan, June 17-23, 200
Multi-Gauge-Boson Vertices and Chiral Lagrangian Parameters in Higgsless Models with Ideal Fermion Delocalization
Higgsless models with fermions whose SU(2) properties are "ideally
delocalized," such that the fermion's probability distribution is appropriately
related to the W boson wavefunction, have been shown to minimize deviations in
precision electroweak parameters. As contributions to the S parameter vanish to
leading order, current constraints on these models arise from limits on
deviations in multi-gauge-boson vertices. We compute the form of the triple and
quartic gauge boson vertices in these models and show that these constraints
provide lower bounds only of order a few hundred GeV on the masses of the
lightest KK resonances. Higgsless models with ideal fermion delocalization
provide an example of extended electroweak gauge interactions with suppressed
couplings of fermions to extra gauge-bosons, and these are the only models for
which triple-gauge-vertex measurements provide meaningful constraints. We
relate the multi-gauge couplings to parameters of the electroweak chiral
Lagrangian, and the parameters obtained in these SU(2) x SU(2) models apply
equally to the corresponding five dimensional gauge theory models of QCD. We
also discuss the collider phenomenology of the KK resonances in models with
ideal delocalization. These resonances are found to be fermiophobic, therefore
traditional direct collider searches are not sensitive to them and measurements
of gauge-boson scattering will be needed to find them.Comment: 28 pages, 1 eps figure. Typo in reference correcte
Identifying Better Effective Higgsless Theories via W_L W_L Scattering
The three site Higgsless model has been offered as a benchmark for studying
the collider phenomenology of Higgsless models. In this talk, we present how
well the three site Higgsless model performs as a general representative of
Higgsless models in describing W_L W_L scattering, and which modifications can
make it more representative. We employ general sum rules relating the masses
and couplings of the Kaluza-Klein (KK) modes of the gauge fields in continuum
and deconstructed Higgsless models as a way to compare the different theories.
After comparing the three site Higgsless model to flat and warped continuum
Higgsless models, we analyze an extensions of the three site Higgsless model,
namely, the Hidden Local Symmetry (HLS) Higgsless model. We demonstrate that
W_LW_L scattering in the HLS Higgsless model can very closely approximate
scattering in the continuum models, provided that the parameter `a' is chosen
to mimic rho-meson dominance of pi-pi scattering in QCD
General Sum Rules for WW Scattering in Higgsless Models: Equivalence Theorem and Deconstruction Identities
We analyze inelastic 2 to 2 scattering amplitudes for gauge bosons and
Nambu-Goldstone bosons in deconstructed Higgsless models. Using the (KK)
Equivalence Theorem in 4D (5D), we derive a set of general sum rules among the
boson masses and multi-boson couplings that are valid for arbitrary
deconstructed models. Taking the continuum limit, our results naturally include
the 5D Higgsless model sum rules for arbitrary 5D geometry and boundary
conditions; they also reduce to the elastic sum rules when applied to the
special case of elastic scattering. For the case of linear deconstructed
Higgsless models, we demonstrate that the sum rules can also be derived from a
set of general deconstruction identities and completeness relations. We apply
these sum rules to the deconstructed 3-site Higgsless model and its extensions;
we show that in 5D ignoring all higher KK modes (n>1) is inconsistent once the
inelastic channels become important. Finally, we discuss how our results
generalize beyond the case of linear Higgsless models.Comment: 36 pages, 2 figure
Deconstruction and Elastic pi pi Scattering in Higgsless Models
We study elastic pion-pion scattering in global linear moose models and apply
the results to a variety of Higgsless models in flat and AdS space using the
Equivalence Theorem. In order to connect the global moose to Higgsless models,
we first introduce a block-spin transformation which corresponds, in the
continuum, to the freedom to perform coordinate transformations in the
Higgsless model. We show that it is possible to make an "f-flat" deconstruction
in which all of the f-constants f_j of the linear moose model are identical;
the phenomenologically relevant f-flat models are those in which the coupling
constants of the groups at either end of the moose are small - corresponding to
the global linear moose. In studying pion-pion scattering, we derive various
sum rules, including one analogous to the KSRF relation, and use them in
evaluating the low-energy and high-energy forms of the leading elastic partial
wave scattering amplitudes. We obtain elastic unitarity bounds as a function of
the mass of the lightest KK mode and discuss their physical significance.Comment: 33 pages, JHEP3. Minor typos correcte
Electroweak Corrections and Unitarity in Linear Moose Models
We calculate the form of the corrections to the electroweak interactions in
the class of Higgsless models which can be "deconstructed'' to a chain of SU(2)
gauge groups adjacent to a chain of U(1) gauge groups, and with the fermions
coupled to any single SU(2) group and to any single U(1) group along the chain.
The primary advantage of our technique is that the size of corrections to
electroweak processes can be directly related to the spectrum of vector bosons
("KK modes"). In Higgsless models, this spectrum is constrained by unitarity.
Our methods also allow for arbitrary background 5-D geometry, spatially
dependent gauge-couplings, and brane kinetic energy terms. We find that, due to
the size of corrections to electroweak processes in any unitary theory,
Higgsless models with localized fermions are disfavored by precision
electroweak data. Although we stress our results as they apply to continuum
Higgsless 5-D models, they apply to any linear moose model including those with
only a few extra vector bosons. Our calculations of electroweak corrections
also apply directly to the electroweak gauge sector of 5-D theories with a bulk
scalar Higgs boson; the constraints arising from unitarity do not apply in this
case.Comment: 50 pages, 11 eps figures, typos correcte
- …