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Curing the Ills of Higgsless Models: the S Parameter and Unitarity
High Energy Physics - Phenomenology · Submitted 13 Sep 2004
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim At the same time the experimental bounds on such Z' and W' gauge bosons become very weak, and their masses can be lowered to make sure that perturbative unitarity is not violated in this theory before reaching energies of several TeV.
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The abstract, sentence by sentence
We consider various constraints on Higgsless models of electroweak symmetry breaking based on a bulk SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group in warped space. First we show that the S parameter which is positive if fermions are localized on the Planck brane can be lowered (or made vanishing) by changing the localization of the light fermions. If the wave function of the light fermions is almost flat their coupling to the gauge boson KK modes will be close to vanishing, and therefore contributions to the S parameter will be suppressed. At the same time the experimental bounds on such Z' and W' gauge bosons become very weak, and their masses can be lowered to make sure that perturbative unitarity is not violated in this theory before reaching energies of several TeV. The biggest difficulty of these models is to incorporate a heavy top quark mass without violating any of the experimental bounds on bottom quark gauge couplings. In the simplest models of fermion masses a sufficiently heavy top quark also implies an unacceptably large correction to the Zb\bar{b} vertex and a large splitting between the KK modes of the top and bottom quarks, yielding large loop corrections to the T-parameter. We present possible directions for model building where perhaps these constraints could be obeyed as well.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We consider various constraints on Higgsless models of electroweak symmetry breaking based on a bulk SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group in warped space. | contribution 0.58 | 0.49 | 0.04 | asserted 0.57 |
| s1 | First we show that the S parameter which is positive if fermions are localized on the Planck brane can be lowered (or made vanishing) by changing the localization of the light fermions. | result 0.90 | 0.89 | 0.25 | asserted 0.99 |
| s2 | If the wave function of the light fermions is almost flat their coupling to the gauge boson KK modes will be close to vanishing, and therefore contributions to the S parameter will be suppressed. | interpretation 0.74 | 0.55 | 0.11 | asserted 0.68 |
| s3 | At the same time the experimental bounds on such Z' and W' gauge bosons become very weak, and their masses can be lowered to make sure that perturbative unitarity is not violated in this theory before reaching energies of several TeV. | result 0.72 | 0.66 | 0.30 | asserted 0.87 |
| s4 | The biggest difficulty of these models is to incorporate a heavy top quark mass without violating any of the experimental bounds on bottom quark gauge couplings. | limitation 0.88 | 0.27 | 0.07 | asserted 1.00 |
| s5 | In the simplest models of fermion masses a sufficiently heavy top quark also implies an unacceptably large correction to the Zb\bar{b} vertex and a large splitting between the KK modes of the top and bottom quarks, yielding large loop corrections to the T-parameter. | limitation 0.51 | 0.19 | 0.05 | asserted 0.99 |
| s6 | We present possible directions for model building where perhaps these constraints could be obeyed as well. | future work 0.84 | 0.59 | 0.15 | hedged possibility 0.96 |
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Original abstract
We consider various constraints on Higgsless models of electroweak symmetry breaking based on a bulk SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group in warped space. First we show that the S parameter which is positive if fermions are localized on the Planck brane can be lowered (or made vanishing) by changing the localization of the light fermions. If the wave function of the light fermions is almost flat their coupling to the gauge boson KK modes will be close to vanishing, and therefore contributions to the S parameter will be suppressed. At the same time the experimental bounds on such Z' and W' gauge bosons become very weak, and their masses can be lowered to make sure that perturbative unitarity is not violated in this theory before reaching energies of several TeV. The biggest difficulty of these models is to incorporate a heavy top quark mass without violating any of the experimental bounds on bottom quark gauge couplings. In the simplest models of fermion masses a sufficiently heavy top quark also implies an unacceptably large correction to the Zb\bar{b} vertex and a large splitting between the KK modes of the top and bottom quarks, yielding large loop corrections to the T-parameter. We present possible directions for model building where perhaps these constraints could be obeyed as well.
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References
How later papers used it
51 later papers cite it
1 later paper by other authors is listed below: 1 used its method or tool.
Uses its method or tool 1 paper
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Implemented its leptons and quarks as in this paper.
Supersymmetric Extensions and Dark Matter in Models of Warped Higgsless EWSB (2008) · 0.81 · paraphrased: the licence does not allow quoting
How the literature uses it
47 arXiv papers cite this in 89 sentences
Papers whose main result relates to this one's
States a conflicting result 1 paper
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However, we find that the entire range of model parameters leads to violation of perturbative unitarity in gauge boson scattering and hence this model is not a reliable perturbative framework.
Higgsless Electroweak Symmetry Breaking in Warped Backgrounds: Constraints and Signatures · 0.81
Papers citing it · 73 sentences without a confident label
Uses its method or tool 1 paper
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The leptons and quarks are implemented as in [ref] .
Supersymmetric Extensions and Dark Matter in Models of Warped Higgsless EWSB · Higgsless Electroweak Symmetry Breaking · 0.81
Compares with it 1 paper
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This is to be contrasted with the proposal of Ref. [ref] , where fermions are de-localized as a way to evade electroweak constraints; as well as with the one of Ref. [ref] , where there is a flavor symmetry in the 5D bulk.
Electroweak Symmetry Breaking from a Holographic Fourth Generation · Conclusions and Outlook · 1.00
Cites it as support 3 papers
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As we demonstrate in the Appendix, this amount of delocalization insures the equality of the tree-level three-site model couplings to those of the standard model, up to corrections of order $x^4$ [ref] and the absence of large tree-level corrections to precision electroweak measurements [ref] .
The Flavor Structure of the Three-Site Higgsless Model · Gauge-Boson Couplings at Tree-Level · 0.96
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The visible excess over the SM estimate at high values of $m_W^+W^-$ results from a residual logarithmic growth of the $VVW^+W^-$ sub-amplitude at invariant masses large compared to the first Kaluza-Klein resonance [ref] .
QCD Corrections to Vector-Boson Fusion Processes in Warped Higgsless Models · Impact of the fermion sector · 0.96
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If the light fermion profiles are almost flat $(c≃1/2)$ then their coupling to the gauge boson Kaluza-Klein modes is vanishingly small thereby suppressing the contributions to the $S$ parameter [ref] .
TASI Lectures on a Holographic View of Beyond the Standard Model Physics · The warped Higgsless model · 0.96
Cites it as background 10 papers
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Higgsless models [ref] of electroweak symmetry breaking provide effective low-energy theories of a strongly-interacting symmetry breaking sector [ref] which, in the case of “delocalized" fermions [ref] , can be consistent with electroweak precision measurements [ref] .
Z to b bbar and Chiral Currents in Higgsless Models · Introduction · 0.98
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In Higgsless models [ref] , the first two neutral resonances are nearly degenerate, and they correspond to the first KK excitation of the $Z$ and of the photon.
Nearby resonances beyond the Breit-Wigner approximation · Numerical example: $Z'$ and $A'$ in Higgsless models · 0.87
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Inspired by the idea that one could maintain perturbative unitarity in extra-dimensional models through heavy vector resonance exchanges in lieu of a Higgs [ref] , Higgsless models were intially introduced in an extra-dimensional context as $SU(2)×SU(2)×U(1)$ gauge theories living in a slice of $AdS_5$, with symmetry breaking codified in the boundary condition of the gauge fields [ref] .
Top-Higgs and Top-pion phenomenology in the Top Triangle Moose model · Introduction · 0.96
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