The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Leonardo Giusti - One of the best experts on this subject based on the ideXlab platform.
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non gaussianities in the Topological Charge distribution of the su 3 yang mills theory
Physical Review D, 2015Co-Authors: Marco Ce, Cristian Consonni, Georg P Engel, Leonardo GiustiAbstract:We study the Topological Charge distribution of the SU(3) Yang--Mills theory with high precision in order to be able to detect deviations from Gaussianity. The computation is carried out on the lattice with high statistics Monte Carlo simulations by implementing a naive discretization of the Topological Charge evolved with the Yang--Mills gradient flow. This definition is far less demanding than the one suggested from Neuberger's fermions and, as shown in this paper, in the continuum limit its cumulants coincide with those of the universal definition appearing in the chiral Ward identities. Thanks to the range of lattice volumes and spacings considered, we can extrapolate the results for the second and fourth cumulant of the Topological Charge distribution to the continuum limit with confidence by keeping finite volume effects negligible with respect to the statistical errors. Our best results for the Topological susceptibility is t_0^2*chi=6.67(7)*10^-4, where t_0 is a standard reference scale, while for the ratio of the forth cumulant over the second we obtain R=0.233(45). The latter is compatible with the expectations from the large Nc expansion, while it rules out the theta-behavior of the vacuum energy predicted by the dilute instanton model. Its large distance from 1 implies that, in the ensemble of gauge configurations that dominate the path integral, the fluctuations of the Topological Charge are of quantum non-perturbative nature.
Jian-bo Zhang - One of the best experts on this subject based on the ideXlab platform.
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Topological Charge evolution in the Markov chain of QCD
Physics Letters B, 2020Co-Authors: Derek B. Leinweber, Anthony G. Williams, Jian-bo ZhangAbstract:Copyright © 2004 Elsevier B.V. All rights reserved. Printed in U.S.A. Submitted to Cornell University’s online archive www.arXiv.org in 2004 by Jianbo Zhang. Post-print sourced from www.arxiv.org.The Topological Charge is studied on lattices of large physical volume and fine lattice spacing. We illustrate how a parity transformation on the SU(3) link-variables of lattice gauge configurations reverses the sign of the Topological Charge and leaves the action invariant. Random applications of the parity transformation are proposed to traverse from one Topological Charge sign to the other. The transformation provides an improved unbiased estimator of the ensemble average and is essential in improving the ergodicity of the Markov chain process.Derek B. Leinweber, Anthony G. Williams, Jian-Bo Zhang and Frank X. Leehttp://www.elsevier.com/wps/find/journaldescription.cws_home/505706/description#descriptio
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Topological Charge evolution in the Markov chain of QCD
Physics Letters B, 2004Co-Authors: Derek B. Leinweber, Anthony G. Williams, Jian-bo ZhangAbstract:The Topological Charge is studied on lattices of large physical volume and fine lattice spacing. We illustrate how a parity transformation on the SU(3) link-variables of lattice gauge configurations reverses the sign of the Topological Charge and leaves the action invariant. Random applications of the parity transformation are proposed to traverse from one Topological Charge sign to the other. The transformation provides an improved unbiased estimator of the ensemble average and is essential in improving the ergodicity of the Markov chain process.
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low dimensional long range Topological Charge structure in the qcd vacuum
Physical Review D, 2003Co-Authors: Ivan Horvath, Terrence Draper, Shaojing Dong, Nilmani Mathur, H Thacker, Jian-bo ZhangAbstract:While sign-coherent 4-dimensional structures cannot dominate Topological Charge fluctuations in the QCD vacuum at all scales due to reflection positivity, it is possible that enhanced coherence exists over extended space-time regions of lower dimension. Using the overlap Dirac operator to calculate Topological Charge density, we present evidence for such structure in pure-glue SU(3) lattice gauge theory. It is found that a typical equilibrium configuration is dominated by two oppositely-Charged sign-coherent connected structures (``sheets'') covering about 80% of space-time. Each sheet is built from elementary 3-d cubes connected through 2-d faces, and approximates a low-dimensional curved manifold (or possibly a fractal structure) embedded in the 4-d space. At the heart of the sheet is a ``skeleton'' formed by about 18% of the most intense space-time points organized into a global long-range structure, involving connected parts spreading over maximal possible distances. We find that the skeleton is locally 1-dimensional and propose that its geometrical properties might be relevant for understanding the possible role of Topological Charge fluctuations in the physics of chiral symmetry breaking.
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The local structure of Topological Charge fluctuations in QCD
Nuclear Physics B - Proceedings Supplements, 2003Co-Authors: I. Horva´th, S.j. Dong, Terrence Draper, Jian-bo Zhang, H.b. ThackerAbstract:We introduce the Dirac eigenmode filtering of Topological Charge density associated with Ginsparg-Wilson fermions as a tool to investigate the local structure of Topological Charge fluctuations in QCD. The resulting framework is used to demonstrate that the bulk of Topological Charge in QCD does not appear in the form of unit quantized lumps. This means that the mixing of ''would-be'' zeromodes associated with such lumps is probably not the prevalent microscopic mechanism for spontaneous chiral symmetry breaking in QCD. To characterize the coherent local behavior in Topological Charge density at low energy, we compute the Charges contained in maximal coherent spheres enclosing non-overlapping peaks. We find a continuous distribution essentially ending at {approx}0.5. Finally, we study, for the first time, the overlap-operator Topological-Charge-density correlators and find consistency with non-positivity at nonzero physical distance. This represents a non-trivial check on the locality (in gauge paths) of the overlap Dirac operator for realistic gauge backgrounds.
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Local structure of Topological Charge fluctuations in QCD
Physical Review D, 2003Co-Authors: Ivan Horvath, H.b. Thacker, S.j. Dong, Terrence Draper, Jian-bo ZhangAbstract:We consider the lattice Topological Charge density introduced by Hasenfratz, Laliena, and Niedermayer and propose its eigenmode expansion as a tool to investigate the structure of Topological Charge fluctuations in QCD. The resulting effective density is built from local chiralities studied previously. At every order of the expansion, the density exactly sums up to the global Topological Charge, and the leading term describes the maximally smooth space-time distribution of Charge relevant for propagating light fermions. We use this framework to demonstrate our previous suggestion that the bulk of the Topological Charge in QCD does not effectively appear in the form of quantized unit lumps. Our conclusion implies that it is unlikely that the mixing of -would-be- zero modes associated with such lumps is the prevalent microscopic mechanism for spontaneous chiral symmetry breaking in QCD. We also present the first results quantitatively characterizing the space-time behavior of effective densities. For coherent fluctuations contained in spherical regions, we find a continuous distribution of associated Charges essentially ending at [approximate] 0.5.
Marco Ce - One of the best experts on this subject based on the ideXlab platform.
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non gaussianities in the Topological Charge distribution of the su 3 yang mills theory
Physical Review D, 2015Co-Authors: Marco Ce, Cristian Consonni, Georg P Engel, Leonardo GiustiAbstract:We study the Topological Charge distribution of the SU(3) Yang--Mills theory with high precision in order to be able to detect deviations from Gaussianity. The computation is carried out on the lattice with high statistics Monte Carlo simulations by implementing a naive discretization of the Topological Charge evolved with the Yang--Mills gradient flow. This definition is far less demanding than the one suggested from Neuberger's fermions and, as shown in this paper, in the continuum limit its cumulants coincide with those of the universal definition appearing in the chiral Ward identities. Thanks to the range of lattice volumes and spacings considered, we can extrapolate the results for the second and fourth cumulant of the Topological Charge distribution to the continuum limit with confidence by keeping finite volume effects negligible with respect to the statistical errors. Our best results for the Topological susceptibility is t_0^2*chi=6.67(7)*10^-4, where t_0 is a standard reference scale, while for the ratio of the forth cumulant over the second we obtain R=0.233(45). The latter is compatible with the expectations from the large Nc expansion, while it rules out the theta-behavior of the vacuum energy predicted by the dilute instanton model. Its large distance from 1 implies that, in the ensemble of gauge configurations that dominate the path integral, the fluctuations of the Topological Charge are of quantum non-perturbative nature.
H.b. Thacker - One of the best experts on this subject based on the ideXlab platform.
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Topological Charge and the Laminar Structure of the QCD Vacuum
arXiv: High Energy Physics - Theory, 2007Co-Authors: H.b. ThackerAbstract:Monte Carlo studies of pure glue SU(3) gauge theory using the overlap‐based Topological Charge operator have revealed a laminar structure in the QCD vacuum consisting of extended, thin, coherent, locally 3‐dimensional sheets of Topological Charge embedded in 4D space, with opposite sign sheets interleaved. In this talk I discuss the interpretation of these Monte Carlo results in terms of our current theoretical understanding of theta‐dependence and Topological structure in asymptotically free gauge theories.
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Coherent Topological Charge structure in CP(N-1) models and QCD
Physical Review D, 2005Co-Authors: Saeed Ahmad, J. Lenaghan, H.b. ThackerAbstract:In an effort to clarify the significance of the recent observation of long-range Topological Charge coherence in QCD gauge configurations, we study the local Topological Charge distributions in two-dimensional CP{sup N-1} sigma models, using the overlap Dirac operator to construct the lattice Topological Charge. We find long-range sign coherence of Topological Charge along extended one-dimensional structures in two-dimensional spacetime. We discuss the connection between the long-range Topological structure found in CP{sup N-1} and the observed sign coherence along three-dimensional sheets in four-dimensional QCD gauge configurations. In both cases, coherent regions of Topological Charge form along membranelike surfaces of codimension one. We show that the Monte Carlo results, for both two-dimensional and four-dimensional gauge theory, support a view of Topological Charge fluctuations suggested by Luescher and Witten. In this framework, the observed membranes are associated with boundaries between ''k-vacua,'' characterized by an effective local value of {theta} which jumps by {+-}2{pi} across the boundary.
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D-branes and Topological Charge in QCD
arXiv: High Energy Physics - Lattice, 2005Co-Authors: H.b. ThackerAbstract:The recently observed long-range coherent structure of Topological Charge fluctuations in QCD is compared with theoretical expectations based on the AdS/CFT brane construction of nonsupersymmetric gauge theory by Witten. Similar observations of coherent TopologicalCharge structure in 2D $CP^{N-1}$ sigma models are interpreted in terms of Wilson lines representing world lines of screened electric Charges. The analogy between 2D U(1) and 4D Yang-Mills theory leads to the interpretation of the observed coherent sheets of Topological Charge in QCD as screened ``Wilson bags'' first suggested by Luscher. The duality between the Wilson bag surface and a wrapped 6-brane in IIA string theory is discussed. The complete screening of the force between bag surfaces for integer values of the bag Charge $\theta/2\pi$ corresponds to the observation by Polchinski that the net force between d-branes from closed string exchange vanishes for quantized values of Ramond-Ramond Charge.
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Topological Charge Membranes in 2D and 4D Gauge Theory
arXiv: High Energy Physics - Lattice, 2005Co-Authors: H.b. Thacker, Saeed Ahmad, J. LenaghanAbstract:Local Topological Charge structure in the 2D CP ( N − 1 ) sigma models is studied using the overlap Dirac operator. Long-range coherence of Topological Charge along locally 1D regions in 2D space-time is observed. We discuss the connection between these results and the recent discovery of coherent 3D sheets of Topological Charge in 4D QCD. In both cases, coherent regions of Topological Charge form along surfaces of approximmate codimension 1.
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The local structure of Topological Charge fluctuations in QCD
Nuclear Physics B - Proceedings Supplements, 2003Co-Authors: I. Horva´th, S.j. Dong, Terrence Draper, Jian-bo Zhang, H.b. ThackerAbstract:We introduce the Dirac eigenmode filtering of Topological Charge density associated with Ginsparg-Wilson fermions as a tool to investigate the local structure of Topological Charge fluctuations in QCD. The resulting framework is used to demonstrate that the bulk of Topological Charge in QCD does not appear in the form of unit quantized lumps. This means that the mixing of ''would-be'' zeromodes associated with such lumps is probably not the prevalent microscopic mechanism for spontaneous chiral symmetry breaking in QCD. To characterize the coherent local behavior in Topological Charge density at low energy, we compute the Charges contained in maximal coherent spheres enclosing non-overlapping peaks. We find a continuous distribution essentially ending at {approx}0.5. Finally, we study, for the first time, the overlap-operator Topological-Charge-density correlators and find consistency with non-positivity at nonzero physical distance. This represents a non-trivial check on the locality (in gauge paths) of the overlap Dirac operator for realistic gauge backgrounds.
Cristian Consonni - One of the best experts on this subject based on the ideXlab platform.
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non gaussianities in the Topological Charge distribution of the su 3 yang mills theory
Physical Review D, 2015Co-Authors: Marco Ce, Cristian Consonni, Georg P Engel, Leonardo GiustiAbstract:We study the Topological Charge distribution of the SU(3) Yang--Mills theory with high precision in order to be able to detect deviations from Gaussianity. The computation is carried out on the lattice with high statistics Monte Carlo simulations by implementing a naive discretization of the Topological Charge evolved with the Yang--Mills gradient flow. This definition is far less demanding than the one suggested from Neuberger's fermions and, as shown in this paper, in the continuum limit its cumulants coincide with those of the universal definition appearing in the chiral Ward identities. Thanks to the range of lattice volumes and spacings considered, we can extrapolate the results for the second and fourth cumulant of the Topological Charge distribution to the continuum limit with confidence by keeping finite volume effects negligible with respect to the statistical errors. Our best results for the Topological susceptibility is t_0^2*chi=6.67(7)*10^-4, where t_0 is a standard reference scale, while for the ratio of the forth cumulant over the second we obtain R=0.233(45). The latter is compatible with the expectations from the large Nc expansion, while it rules out the theta-behavior of the vacuum energy predicted by the dilute instanton model. Its large distance from 1 implies that, in the ensemble of gauge configurations that dominate the path integral, the fluctuations of the Topological Charge are of quantum non-perturbative nature.
