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Author ![sorted by Author field, ascending order (up)](img/sort_asc.gif) |
Aguiar, P.; Rafecas, M.; Ortuño, J.E.; Kontaxakis, G.; Santos, A.; Pavia, J.; Rosetti, M. |
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Title |
Geometrical and Monte Carlo projectors in 3D PET reconstruction |
Type |
Journal Article |
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Year |
2010 |
Publication |
Medical Physics |
Abbreviated Journal |
Med. Phys. |
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Volume |
37 |
Issue |
11 |
Pages |
5691-5702 |
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Keywords |
3D PET; iterative reconstruction; list-mode reconstruction; ray-tracing techniques; Monte Carlo simulation; system response matrix |
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Abstract |
Purpose: In the present work, the authors compare geometrical and Monte Carlo projectors in detail. The geometrical projectors considered were the conventional geometrical Siddon ray-tracer (S-RT) and the orthogonal distance-based ray-tracer (OD-RT), based on computing the orthogonal distance from the center of image voxel to the line-of-response. A comparison of these geometrical projectors was performed using different point spread function (PSF) models. The Monte Carlo-based method under consideration involves an extensive model of the system response matrix based on Monte Carlo simulations and is computed off-line and stored on disk. Methods: Comparisons were performed using simulated and experimental data of the commercial small animal PET scanner rPET. Results: The results demonstrate that the orthogonal distance-based ray-tracer and Siddon ray-tracer using PSF image-space convolutions yield better images in terms of contrast and spatial resolution than those obtained after using the conventional method and the multiray-based S-RT. Furthermore, the Monte Carlo-based method yields slight improvements in terms of contrast and spatial resolution with respect to these geometrical projectors. Conclusions: The orthogonal distance-based ray-tracer and Siddon ray-tracer using PSF image-space convolutions represent satisfactory alternatives to factorizing the system matrix or to the conventional on-the-fly ray-tracing methods for list-mode reconstruction, where an extensive modeling based on Monte Carlo simulations is unfeasible. |
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Address |
[Aguiar, Pablo] Univ Santiago de Compostela, Dept Fis Particulas, Complexo Hosp Univ Santiago de Compostela, Fdn IDICHUS IDIS, Santiago De Compostela, Spain, Email: pablo.aguiar.fernandez@sergas.es |
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Amer Assoc Physicists Medicine Amer Inst Physics |
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English |
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ISSN |
0094-2405 |
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Notes |
ISI:000283747600015 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
no |
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Call Number |
IFIC @ elepoucu @ |
Serial |
338 |
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Author ![sorted by Author field, ascending order (up)](img/sort_asc.gif) |
Aguilar, A.C.; Binosi, D.; Papavassiliou, J. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
The gluon mass generation mechanism: A concise primer |
Type |
Journal Article |
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Year |
2016 |
Publication |
Frontiers of Physics |
Abbreviated Journal |
Front. Phys. |
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Volume |
11 |
Issue |
2 |
Pages |
111203 - 18pp |
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Keywords |
nonperturbative physics; Schwinger-Dyson equations; dynamical mass generation |
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Abstract |
We present a pedagogical overview of the nonperturbative mechanism that endows gluons with a dynamical mass. This analysis is performed based on pure Yang-Mills theories in the Landau gauge, within the theoretical framework that emerges from the combination of the pinch technique with the background field method. In particular, we concentrate on the Schwinger-Dyson equation satisfied by the gluon propagator and examine the necessary conditions for obtaining finite solutions within the infrared region. The role of seagull diagrams receives particular attention, as do the identities that enforce the cancellation of all potential quadratic divergences. We stress the necessity of introducing nonperturbative massless poles in the fully dressed vertices of the theory in order to trigger the Schwinger mechanism, and explain in detail the instrumental role of these poles in maintaining the Becchi-Rouet-Stora-Tyutin symmetry at every step of the mass-generating procedure. The dynamical equation governing the evolution of the gluon mass is derived, and its solutions are determined numerically following implementation of a set of simplifying assumptions. The obtained mass function is positive definite, and exhibits a power law running that is consistent with general arguments based on the operator product expansion in the ultraviolet region. A possible connection between confinement and the presence of an inflection point in the gluon propagator is briefly discussed. |
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Address |
[Aguilar, A. C.] Univ Campinas UNICAMP, Gleb Wataghin Inst Phys, BR-13083859 Campinas, SP, Brazil, Email: Joannis.Papavassiliou@uv.es |
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Publisher |
Higher Education Press |
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English |
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ISSN |
2095-0462 |
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Notes |
WOS:000387550300001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
2859 |
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Author ![sorted by Author field, ascending order (up)](img/sort_asc.gif) |
Aguilar, A.C.; Binosi, D.; Papavassiliou, J. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Gluon mass through ghost synergy |
Type |
Journal Article |
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Year |
2012 |
Publication |
Journal of High Energy Physics |
Abbreviated Journal |
J. High Energy Phys. |
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Volume |
01 |
Issue |
1 |
Pages |
050 - 32pp |
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Keywords |
Nonperturbative Effects; QCD |
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Abstract |
In this work we compute, at the “one-loop-dressed” level, the nonperturbative contribution of the ghost loops to the self-energy of the gluon propagator, in the Landau gauge. This is accomplished within the PT-BFM formalism, where the contribution of the ghost-loops is inherently transverse, by virtue of the QED-like Ward identities satisfied in this framework. At the level of the “one-loop dressed” approximation, the ghost transversality is preserved by employing a suitable gauge-technique Ansatz for the longitudinal part of the full ghost-gluon vertex. Under the key assumption that the undetermined transverse part of this vertex is numerically subleading in the infrared, and using as nonperturbative input the available lattice data for the ghost dressing function, we show that the ghost contributions have a rather sizable effect on the overall shape of the gluon propagator, both for d = 3, 4. Then, by exploiting a recently introduced dynamical equation for the effective gluon mass, whose solutions depend crucially on the characteristics of the gluon propagator at intermediate energies, we show that if the ghost loops are removed from the gluon propagator then the gluon mass vanishes. These findings suggest that, at least at the level of the Schwinger-Dyson equations, the effects of gluons and ghosts are inextricably connected, and must be combined suitably in order to reproduce the results obtained in the recent lattice simulations. |
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Address |
[Aguilar, A. C.] Fed Univ ABC, CCNH, BR-09210170 Santo Andre, Brazil, Email: arlene.aguilar@ufabc.edu.br |
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Thesis |
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Publisher |
Springer |
Place of Publication |
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English |
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ISSN |
1126-6708 |
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Conference |
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Notes |
WOS:000300181800050 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
969 |
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Permanent link to this record |
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Author ![sorted by Author field, ascending order (up)](img/sort_asc.gif) |
Aguilar, A.C.; Binosi, D.; Papavassiliou, J. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
QCD effective charges from lattice data |
Type |
Journal Article |
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Year |
2010 |
Publication |
Journal of High Energy Physics |
Abbreviated Journal |
J. High Energy Phys. |
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Volume |
07 |
Issue |
7 |
Pages |
002 - 24pp |
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Keywords |
Nonperturbative Effects; QCD |
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Abstract |
We use recent lattice data on the gluon and ghost propagators, as well as the Kugo-Ojima function, in order to extract the non-perturbative behavior of two particular definitions of the QCD effective charge, one based on the pinch technique construction, and one obtained from the standard ghost-gluon vertex. The construction relies crucially on the definition of two dimensionful quantities, which are invariant under the renormalization group, and are built out of very particular combinations of the aforementioned Green's functions. The main non-perturbative feature of both effective charges, encoded in the infrared finiteness of the gluon propagator and ghost dressing function used in their definition, is the freezing at a common finite (non-vanishing) value, in agreement with a plethora of theoretical and phenomenological expectations. We discuss the sizable discrepancy between the freezing values obtained from the present lattice analysis and the corresponding estimates derived from several phenomenological studies, and attribute its origin to the difference in the gauges employed. A particular toy calculation suggests that the modifications induced to the non-perturbative gluon propagator by the gauge choice may indeed account for the observed deviation of the freezing values. |
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Address |
[Aguilar, A. C.] Fed Univ ABC, CCNH, BR-09210170 Santo Andre, Brazil, Email: arlene.aguilar@ufabc.edu.br |
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Thesis |
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Publisher |
Springer |
Place of Publication |
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English |
Summary Language |
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ISSN |
1126-6708 |
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Notes |
ISI:000281504500002 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ elepoucu @ |
Serial |
384 |
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Permanent link to this record |
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Author ![sorted by Author field, ascending order (up)](img/sort_asc.gif) |
Aguilar, A.C.; De Soto, F.; Ferreira, M.N.; Papavassiliou, J.; Pinto-Gomez, F.; Roberts, C.D.; Rodriguez-Quintero, J. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Schwinger mechanism for gluons from lattice QCD |
Type |
Journal Article |
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Year |
2023 |
Publication |
Physics Letters B |
Abbreviated Journal |
Phys. Lett. B |
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Volume |
841 |
Issue |
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Pages |
137906 - 8pp |
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Keywords |
Continuum Schwinger function methods; Emergence of mass; Gluons; Lattice Schwinger function methods; Quantum chromodynamics; Schwinger mechanism of gauge boson mass; generation |
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Abstract |
Continuum and lattice analyses have revealed the existence of a mass-scale in the gluon two-point Schwinger function. It has long been conjectured that this expresses the action of a Schwinger mechanism for gauge boson mass generation in quantum chromodynamics (QCD). For such to be true, it is necessary and sufficient that a dynamically-generated, massless, colour-carrying, scalar gluon+gluon correlation emerges as a feature of the dressed three-gluon vertex. Working with results on elementary Schwinger functions obtained via the numerical simulation of lattice-regularised QCD, we establish with an extremely high level of confidence that just such a feature appears; hence, confirm the conjectured origin of the gluon mass scale. |
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Address |
[Aguilar, A. C.] Univ Estadual Campinas, Inst Phys Gleb Wataghin, UNICAMP, BR-13083859 Campinas, SP, Brazil, Email: cristina.aguilar@unicamp.br; |
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Corporate Author |
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Thesis |
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Publisher |
Elsevier |
Place of Publication |
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Editor |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0370-2693 |
ISBN |
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Expedition |
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Conference |
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Notes |
WOS:000984221700001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5530 |
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Permanent link to this record |