Possible experimental signatures at the CERN LHC of strongly interacting electroweak symmetry breaking

Fabbrichesi, Marco; Vecchi, Luca

doi:10.1103/physrevd.76.056002

Cited by 13 publications

(20 citation statements)

References 54 publications

(57 reference statements)

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“…Due to the equivalence theorem this scattering is mapped directly into the pion-pion scattering of the underlying strongly coupled gauge theory driving the breaking of the electroweak theory. A similar analysis has been performed in [29]. We have shown that there are regions in the parameters space of these models, allowed by the electroweak precision data, according to which tree-level unitarity is delayed up to around 3-4 TeV without the inclusion of any sub-TeV resonances.…”

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confidence: 59%

WWscattering in walking technicolor: No discovery scenarios at the CERN LHC and ILC

Foadi¹,

Sannino

2008

Phys. Rev. D

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We analyze the W W scattering in scenarios of dynamical electroweak symmetry breaking of walking technicolor type. We show that in these theories there are regions of the parameters space allowed by the electroweak precision data, in which unitarity violation is delayed at tree level up to around 3-4 TeV without the inclusion of any sub-TeV resonances.The simplest argument often used to predict the existence of yet undiscovered particles at the TeV scale comes from unitarity of longitudinal gauge boson scattering amplitudes. If the electroweak symmetry breaking sector (EWSB) is weakly interacting, unitarity implies that new particle states must show up below 1 TeV, being these spin-0 isosinglets (the Higgs boson) or spin-1 isotriplets (e.g. Kaluza-Klein modes). A strongly interacting EWSB sector can however change this picture, because of the strong coupling between the pions (eaten by the longitudinal components of the standard model gauge bosons) and the other bound states of the strongly interacting sector. An illuminating example comes from QCD. In Ref.[1] it was shown that for six colors or more, the 770 GeV ρ meson is enough to delay the onset of unitarity violation of the pion-pion scattering amplitude up to well beyond 1 GeV. Here the 't Hooft large N limit was used, however an even lower number of colors is needed to reach a similar delay of unitarity violation when an alternative large N limit is used [2]. Scaling up to the electroweak scale, this translates in a 1.5 TeV techni-ρ being able to delay unitarity violation of longitudinal gauge boson scattering amplitudes up to 4 TeV or more. Such a particle would be harder to be discovered at the LHC and ILC. Such a model, however, would not be realistic for other reasons: a large contribution to the S parameter [3], and large flavor changing neutral currents (FCNC) if the ordinary fermions acquire mass via an old fashioned extended technicolor sector (ETC), to mention the most relevant ones.Walking Technicolor (WT) [4,5,6] provides a natural framework to address these problems. In fact walking dynamics helps suppressing FCNC without preventing ETC from yielding realistic fermion masses. Notice that it is always possible to resort to new scalars to give mass to the ordinary fermions while having technicolor only in the gauge sector, or even marry technicolor with supersymmetry [7,8,9,10,11,12,13,14]. Furthermore certain WT models are in agreement with the constraints imposed by electroweak precision data (EWPD) [15,16,17], since the walking dynamics itself naturally lowers the contribution to the S parameter relative to a running theory [18]. Besides, new leptonic sectors [17], which may be needed to avoid possible Witten topological anomalies, can render the overall S parameter negative. The contributions from these sectors, not gauged under the technicolor gauge group, are calculable to any order in perturbation theory. A relevant question to ask is whether a walking regime can be achieved with a sufficiently small number of fermions. In the context of ...

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confidence: 59%

WWscattering in walking technicolor: No discovery scenarios at the CERN LHC and ILC

Foadi¹,

Sannino

2008

Phys. Rev. D

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“…Bounds on the dimension-4 parameter in the ChL lagrangian compatible with precision electroweak constraints have been obtained in [7]. On Fig.…”

Section: Electroweak Constraints On the Chl Paramètersmentioning

confidence: 99%

“…The size of the coefficients OE4,OE5, describing the relevant dynamics of VBS at high energy in the effective ChL description can be given bounds by reasonable assumptions based on different models of the strongly interacting sector, as discussed in [7], and model-independent constraints as discussed in this section. In [7] the values are compared with LHC sensitivity and they seem to faH in the region where LHC is not sensible to this type of processes.…”

Section: Electroweak Constraints On the Chl Paramètersmentioning

confidence: 99%

“…In [7] the values are compared with LHC sensitivity and they seem to faH in the region where LHC is not sensible to this type of processes. Therefore, the presence of vector and scalar resonances required by unitarity will be the only plausible characteristic signatures to look for at the LHC.…”

Section: Electroweak Constraints On the Chl Paramètersmentioning

confidence: 99%

“…13 Region allowed by electroweak precision measurements for a4, a5 parameters [7] (in gray). Aiso causality constraints are shown.…”

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confidence: 99%

See 2 more Smart Citations

Vector Boson Scattering at High Energy at the LHC

Idárraga

Azuelos

Delsart

2007

Fundamental Interactions

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Strong Gauge Boson Scattering at the LHC

Rindani

2009

Physics at the Large Hadron Collider

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In the standard model with electroweak symmetry breaking through the Higgs mechanism, electroweak gauge-boson scattering amplitudes are large if the Higgs boson is heavy, and electroweak gauge interactions become strong. In theories with electroweak symmetry breaking through alternative mechanisms, there could be a strongly interacting gauge sector, possibly with resonances in an accessible energy region. In general, the scattering of longitudinally polarized massive gauge bosons can give information on the mechanism of spontaneous symmetry breaking. At energies below the symmetry breaking scale, the equivalence theorem relates the scattering amplitudes to those of the "would-be" Goldstone modes. In the absence of Higgs bosons, unitarity would be restored by some new physics which can be studied through W W scattering. Some representatives models are discussed. Isolating W W scattering at a hadron collider from other contributions involving W emission from parton lines needs a good understanding of the backgrounds. Resonances, if they exist below about a TeV, would be feasible of observation at the LHC.

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Possible experimental signatures at the CERN LHC of strongly interacting electroweak symmetry breaking

Cited by 13 publications

References 54 publications

WWscattering in walking technicolor: No discovery scenarios at the CERN LHC and ILC

WWscattering in walking technicolor: No discovery scenarios at the CERN LHC and ILC

Vector Boson Scattering at High Energy at the LHC

Strong Gauge Boson Scattering at the LHC

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