Search results for "VERTEX"
showing 10 items of 225 documents
Dynamics for a 2-vertex Quantum Gravity Model
2010
We use the recently introduced U(N) framework for loop quantum gravity to study the dynamics of spin network states on the simplest class of graphs: two vertices linked with an arbitrary number N of edges. Such graphs represent two regions, in and out, separated by a boundary surface. We study the algebraic structure of the Hilbert space of spin networks from the U(N) perspective. In particular, we describe the algebra of operators acting on that space and discuss their relation to the standard holonomy operator of loop quantum gravity. Furthermore, we show that it is possible to make the restriction to the isotropic/homogeneous sector of the model by imposing the invariance under a global …
Unitary chiral dynamics in decays and the role of scalar mesons
2004
We make a theoretical study of the J/psi decays into omegapipi, phipipi, omegaK (K) over bar and phiK (K) over bar using the techniques of the chiral unitary approach stressing the important role of the scalar resonances dynamically generated through the final state interaction of the two pseudoscalar mesons. We also discuss the importance of new mechanisms with intermediate exchange of vector and axial-vector mesons and the role played by the OZI rule in the J/ psi phipipi vertex, quantifying its effects. The results nicely reproduce the experimental data for the invariant mass distributions in all the channels considered. (C) 2004 Elsevier B.V. All rights reserved.
The low lying scalar resonances in the D0 decays into Ks0 and f0(500), f0(980), a0(980)
2015
Abstract The D 0 decay into K s 0 and a scalar resonance, f 0 ( 500 ) , f 0 ( 980 ) , a 0 ( 980 ) , are studied obtaining the scalar resonances from final state interaction of a pair of mesons produced in a first step in the D 0 decay into K s 0 and the pair of pseudoscalar mesons. This weak decay is very appropriate for this kind of study because it allows to produce the three resonances in the same decay in a process that is Cabibbo-allowed, hence the rates obtained are large compared to those of B ¯ 0 decays into J / ψ and a scalar meson that have at least one Cabibbo-suppressed vertex. Concretely the a 0 ( 980 ) production is Cabibbo-allowed here, while it cannot be seen in the B ¯ s 0 …
Infrared finite ghost propagator in the Feynman gauge
2007
We demonstrate how to obtain from the Schwinger-Dyson equations of QCD an infrared finite ghost propagator in the Feynman gauge. The key ingredient in this construction is the longitudinal form factor of the non-perturbative gluon-ghost vertex, which, contrary to what happens in the Landau gauge, contributes non-trivially to the gap equation of the ghost. The detailed study of the corresponding vertex equation reveals that in the presence of a dynamical infrared cutoff this form factor remains finite in the limit of vanishing ghost momentum. This, in turn, allows the ghost self-energy to reach a finite value in the infrared, without having to assume any additional properties for the gluon-g…
Quark mass dependence of the one-loop three-gluon vertex in arbitrary dimension
2001
The one-loop off-shell massive quark contribution to the three-gluon vertex is calculated in an arbitrary space-time dimension. The results for all relevant on-shell and symmetric limits are obtained directly from the general off-shell results. The analytic structure of the results for the relevant massive scalar integrals is also discussed.
Single bottom quark production in kT-factorisation
2015
Journal of High Energy Physics 2015.9 (2015): 123 reproduced by permission of Scuola Internazionale Superiore di Studi Avanzati (SISSA)
Dynamically screened vertex correction to $GW$
2020
Diagrammatic perturbation theory is a powerful tool for the investigation of interacting many-body systems, the self-energy operator $\mathrm{\ensuremath{\Sigma}}$ encoding all the variety of scattering processes. In the simplest scenario of correlated electrons described by the $GW$ approximation for the electron self-energy, a particle transfers a part of its energy to neutral excitations. Higher-order (in screened Coulomb interaction $W$) self-energy diagrams lead to improved electron spectral functions (SFs) by taking more complicated scattering channels into account and by adding corrections to lower order self-energy terms. However, they also may lead to unphysical negative spectral f…
Measurement of the tt¯Z and tt¯W cross sections in proton-proton collisions at s=13 TeV with the ATLAS detector
2019
A measurement of the associated production of a top-quark pair (tt) with a vector boson (W, Z) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented, using 36.1 fb-1 of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. Events are selected in channels with two same- or opposite-sign leptons (electrons or muons), three leptons or four leptons, and each channel is further divided into multiple regions to maximize the sensitivity of the measurement. The ttZ and ttW production cross sections are simultaneously measured using a combined fit to all regions. The best-fit values of the production cross sections are σttZ=0.95±0.08stat±0.10syst…
Online Data Reduction using Track and Vertex Reconstruction on GPUs for the Mu3e Experiment
2017
The Mu3e experiment searches for the lepton flavour violating decay μ + → e + e − e + , aiming to achieve a sensitivity of 2 · 10 −15 in its first phase and ultimately aspiring to a final sensitivity of 10 −16 . During the first phase of the experiment, a muon rate of ∼ 10 8 μ /s will be available, resulting in a data rate of ∼ 80 Gbit/s. The trigger-less readout system is based on optical links and switching FPGAs sending the complete detector data for a time slice to one node of the filter farm. A full online reconstruction is necessary to reduce the data rate to a manageable amount to be written to disk. Graphics processing units (GPUs) are used to fit tracks with a non-iterative 3D trac…
Finite renormalization effects in the induceds¯dHvertex
1986
The finite renormalization contributions to the s-bard-italicH-italic vertex are examined in the standard model. They are explicitly shown to cancel each other among diagrams, so that the lower bound on the Higgs-boson mass M-italic/sub H-italic/>325 MeV is not affected by such effects.