Effective coupling constant in QCD

Espriu, D.; Pascual, P.; Tarrach, R.

doi:10.1088/0305-4616/7/12/007

Cited by 52 publications

(138 citation statements)

References 7 publications

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“…23 Over the last twenty years there has been an ongoing effort to address in a systematic way the low energy sector of hadronic physics, and in particular the sector containing light quarks only via chiral perturbation theory (χPT). The idea is to incorporate SχSB, the Goldstone pions and current algebra, and the ensuing low energy theorems via effective Lagrangians [194,195] which will manifest the desired symmetries and which are written in terms of the pionic fields only. Then one uses these chiral Lagrangians to perform a systematic expansion in the external momenta of the problem, and/or the pion mass divided by some "hadronic scale" usually taken to be 4πf π .…”

Section: Qcd Inequalities Forqq Potentials Quark Masses and Weak Trmentioning

confidence: 99%

QCD inequalities

Nussinov

Lampert

2002

Physics Reports

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Section: Qcd Inequalities Forqq Potentials Quark Masses and Weak Trmentioning

confidence: 99%

QCD inequalities

Nussinov

Lampert

2002

Physics Reports

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“…The EChL formalism has been applied to constrain the effective couplings from EW low energy data. For instance, the couplings a 0 , a 1 and a 8 contribute to the gauge boson self energies up to order q 2 [18], and are related to the T,S and U parameters [14,3,19] as explained below. A one-loop EChL calculation of the self-energy combinations entering the definition of S, T and U gives…”

Section: Chiral Lagrangian Description Of Electroweak Interactionsmentioning

confidence: 99%

“…At LEP-II and Tevatron, three more effective couplings a 2 , a 3 and a 9 come into play, through their contribution to the triple gauge boson vertices. A complete 1-loop EChL calculation [19] and a fit to the data could place constraints on these new couplings, but this analysis has not been done so far. In spite of that, indirect bounds [21,22] of the order of 10 −1 for a 2 , a 3 and a 9 and in the range of 10 −1 to 10 −2 for a 4 , a 5 , a 6 , a 7 and a 10 that contribute to the quartic gauge boson vertices, can be obtained from the low energy data through their contribution to anomalous vertices in 1-loop calculations.…”

Section: Chiral Lagrangian Description Of Electroweak Interactionsmentioning

confidence: 99%

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CERN LHC sensitivity to the resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector

et al. 2000

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We present a unified analysis of the two main production processes of vector boson pairs at the CERN LHC, VV-fusion and qq annihilation, in a minimal strongly interacting electroweak symmetry breaking sector. Using a unitarized electroweak chiral Lagrangian formalism and modeling the final V L V L strong rescattering effects by a form factor, we describe qq annihilation processes in terms of the two chiral parameters that govern elastic V L V L scattering. Depending on the values of these two chiral parameters, the unitarized amplitudes may present resonant enhancements in different angular momentum-isospin channels. Scanning this two parameter space, we generate the general resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector and determine the regions that can be probed at the CERN LHC.

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“…This does a fair job of reproducing those L i 's which happen to correspond to convergent loop integrals [5]. A more sophisticated quark-based approach leads to the extraction of all ten parameters [6]. Most convenient for our purposes is the gauged nonlocal constituent (GNC) quark model [7], which incorporates the momentum dependence expected for dynamically generated fermion masses.…”

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confidence: 99%

Size of flavor-changing effects induced by the symmetry-breaking sector

Holdom

1997

Phys. Rev. D

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It has recently been shown that strong interactions underlying electroweak symmetry breaking will induce four-fermion amplitudes proportional to m t 2 , which in turn will influence a variety of flavor-changing processes. We argue that the typical size of these effects is likely to be far below the current experimental bounds. ͓S0556-2821͑97͒04921-7͔PACS number͑s͒: 12.60. Fr, 12.39.Fe The corrections induced by a new strong sector underlying electroweak symmetry breaking are conveniently encoded in an effective chiral Lagrangian. Recently attention has focused on a particular term in this effective Lagrangian which induces corrections proportional to m t 2 in charged current interactions ͓1͔. Integrating out the t quark then yields interesting effects in the down-type quark sector, inducing corrections to R b and B d 0 -B d 0 mixing ͓1͔, and various rare B and K decays ͓2͔. All these effects are correlated since they are related to one parameter in the effective Lagrangian ͓2͔.In this work we will provide an estimate of the size of the new parameter, expressed in terms of the number of new fermion doublets in some underlying theory of electroweak symmetry breaking. Such an estimate in the case of the S parameter proved useful to constrain technicolor theories. The S parameter is related to a term in an effective Lagrangian with coefficient L 10 ϭϪS/16 which is completely analogous to the L 10 QCD term appearing at order p 4 in the low energy QCD chiral Lagrangian ͓3͔. Since L 10 QCD is a measured quantity, an estimate for S is thereby obtained ͓4͔ for QCD-like technicolor theories.The situation is somewhat different for the parameter of interest here, which is the coefficient of another term appearing at order p 4 . In the QCD case this coefficient is not a measurable quantity since the term can be removed by the equations of motion. Fortunately in the QCD case there are quark models which model the chiral symmetry breaking and which quite successfully reproduce the values of all ten measured parameters, L 1 -L 10 . Such models can then be expected to provide a reasonable estimate of the new parameter, which we will refer to as L 11 ͑corresponding to a 11 in ͓1͔ and ␣ 11 in ͓2͔͒.A naive quark model may be based on the nonlinear model where effects of a single quark loop are considered. This does a fair job of reproducing those L i 's which happen to correspond to convergent loop integrals ͓5͔. A more sophisticated quark-based approach leads to the extraction of all ten parameters ͓6͔. Most convenient for our purposes is the gauged nonlocal constituent ͑GNC͒ quark model ͓7͔, which incorporates the momentum dependence expected for dynamically generated fermion masses. In QCD the mass function is known to fall as the square of the momentum ͑up to logarithms͒ for large momentum. The GNC model can incorporate such momentum dependence in a manner which preserves the local chiral symmetries of the underlying theory. The mass function then naturally regulates the loop integrals, and successful values for L 1 -L 10 are...

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Effective coupling constant in QCD

Cited by 52 publications

References 7 publications

QCD inequalities

QCD inequalities

CERN LHC sensitivity to the resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector

Size of flavor-changing effects induced by the symmetry-breaking sector

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