Abdou Abdel-Rehim - Academia.edu (original) (raw)

Papers by Abdou Abdel-Rehim

Research paper thumbnail of Adaptive method for multicriteria optimization of intensity-modulated proton therapy

Medical Physics, 2018

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Research paper thumbnail of The pion form factor from twisted-mass lattice quantum chromodynamics

Canadian Journal of Physics, 2006

The pion form factor offers insight into the transition from perturbative to nonperturbative quan... more The pion form factor offers insight into the transition from perturbative to nonperturbative quantum chromodynamics (QCD), and is of current experimental interest. Twisted-mass lattice QCD is a method for eliminating unphysical zero modes from Wilson lattice simulations; it also allows for removal of the leading lattice spacing artifacts through a momentum-averaging prescription. In our study of the pion form factor, we performed the first explicit computation with momentum averaging in twisted-mass lattice QCD, and the first use of the GMRES-DR algorithm for twisted fermion matrix inversion.PACS No.: 12.38.Gc

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Research paper thumbnail of The Scalar Sector and the Eta -\u3e 3 Pi Problem

First, recent work on light scalar mesons, which is of possible interest in connection with the s... more First, recent work on light scalar mesons, which is of possible interest in connection with the strong coupling region of QCD is briefly discussed. Then a very short highlighting of a paper concerned with an application to the eta -\u3e 3 pi problem is presented

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Research paper thumbnail of Lattice QCD with a twisted mass term and a strange quark

The European Physical Journal A, 2007

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Research paper thumbnail of Nucleon electromagnetic form factors from twisted mass lattice QCD

Results on the electromagnetic form factors of the nucleon using twisted mass fermion configurati... more Results on the electromagnetic form factors of the nucleon using twisted mass fermion configurations are presented. These include a gauge field ensemble simulated with two degenerate light quarks yielding a pion mass of around 130 MeV, as well as two ensembles that include strange and charm quarks in the sea yielding pion masses of 210 MeV and 373 MeV. Details of the methods used and systematic errors are discussed, such as noise reduction techniques and the effect of excited states contamination.

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Research paper thumbnail of Improved Seed Methods for Symmetric Positive Definite Linear Equations with Multiple Right-hand Sides

We consider symmetric positive definite systems of linear equations with multiple right-hand side... more We consider symmetric positive definite systems of linear equations with multiple right-hand sides. The seed conjugate gradient method solves one right-hand side with the conjugate gradient method and simultaneously projects over the Krylov subspace thus developed for the other right-hand sides. Then the next system is solved and used to seed the remaining ones. Rounding error in the conjugate gradient method limits how much the seeding can improve convergence. We propose three changes to the seed conjugate gradient method: only the first right-hand side is used for seeding, this system is solved past convergence, and the roundoff error is controlled with some reorthogonalization. We will show that results are actually better with only one seeding, even in the case of related right-hand sides. Controlling rounding error gives the potential for rapid convergence for the second and subsequent right-hand sides.

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Research paper thumbnail of Deflated and restarted symmetric Lanczos methods for eigenvalues and linear equations with multiple right-hand sides

A deflated restarted Lanczos algorithm is given for both solving symmetric linear equations and c... more A deflated restarted Lanczos algorithm is given for both solving symmetric linear equations and computing eigenvalues and eigenvectors. The restarting limits the storage so that finding eigenvectors is practical. Meanwhile, the deflating from the presence of the eigenvectors allows the linear equations to generally have good convergence in spite of the restarting. Some reorthogonalization is necessary to control roundoff error, and several approaches are discussed. The eigenvectors generated while solving the linear equations can be used to help solve systems with multiple right-hand sides. Experiments are given with large matrices from quantum chromodynamics that have many right-hand sides.

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Research paper thumbnail of Computation of correlation matrices for tetraquark candidates with J^P = 0^+ and flavor structure q_1 q̅_̅2̅ q_3 q̅_3

The conjecture that several recently observed mesons have a structure, which is not dominated by ... more The conjecture that several recently observed mesons have a structure, which is not dominated by an ordinary quark-antiquark pair, but by a four-quark structure, is being actively investigated both theoretical and experimentally. Such a state may be characterized as a mesonic molecule or as a diquark-antidiquark pair. Lattice QCD provides a theoretically sound framework to study such states. To quantitatively investigate the internal structure of such mesons, one needs to precisely compute correlation matrices containing several interpolating operators including two and four quarks. Here we discuss certain technical aspects of such correlation matrices suited to study tetraquark candidates with J^P = 0^+ and flavor structure q_1 q̅_̅2̅ q_3 q̅_3, e.g. the a_0(980) meson, the D_s0^∗ meson and some of the charged c c̅ X states. Some numerical results for the a_0(980) meson are presented.

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Research paper thumbnail of Investigation of light and heavy tetraquark candidates using lattice QCD

We review the status of an ongoing long-term lattice investigation of the spectrum and structure ... more We review the status of an ongoing long-term lattice investigation of the spectrum and structure of tetraquark candidates. We focus on the light scalar meson a_0(980). First steps regarding the study of a possibly existing c c c̅c̅ tetraquark are also outlined.

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Research paper thumbnail of THE SCALAR SECTOR AND THE η → 3pi PROBLEM

This Article is brought to you for free and open access by the College of Arts and Sciences at SU... more This Article is brought to you for free and open access by the College of Arts and Sciences at SURFACE. It has been accepted for inclusion in Physics by

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Research paper thumbnail of Problems with Multiple Right-Hand

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Research paper thumbnail of Investigation of the tetraquark candidate a0(980): Technical aspects and preliminary results

arXiv: High Energy Physics - Lattice, 2014

We discuss technical aspects and first results of a lattice QCD study of the a0(980) state. We em... more We discuss technical aspects and first results of a lattice QCD study of the a0(980) state. We employ various interpolating operators of quark-antiquark, mesonic molecule, diquark-antidiquark and two-meson type. Both connected and disconnected contributions including diagrams with closed fermion loops are computed. To keep statistical errors small, it is essential to optimize the computation of these diagrams by choosing that combination of techniques most appropriate for each type of diagram from the correlation matrix of interpolating operators. We illustrate, how this can be done, by discussing certain diagrams in detail. We also present preliminary results corresponding to a 4 4 submatrix computed with 2+1 flavors of clover fermions.

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Research paper thumbnail of The hadron spectrum from twisted mass QCD with a strange quark

arXiv: High Energy Physics - Lattice, 2005

Various suggestions exist for incorporating the strange quark into twisted mass QCD. One option f... more Various suggestions exist for incorporating the strange quark into twisted mass QCD. One option for quenched simulations is to employ two twisted doublets, (u,d) and (c,s), with separate twist angles. Working in the isospin limit, preliminary results for the quenched spectrum of strange hadrons are presented, with both twist angles tuned to pi/2. Splittings within the mass multiplets provide some insight into the symmetry breaking effects of twisted mass lattice QCD.

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Research paper thumbnail of Effects of Light Scalar Mesons in eta -> 3pi decay

We study the role of a possible nonet of light scalar mesons in the still interesting [eta] ->... more We study the role of a possible nonet of light scalar mesons in the still interesting [eta] -> 3[p]i decay process, with the primary motivation of learning more about the scalars themselves. The framework is a conventional non-linear chiral Lagrangian of pseudoscalars and vectors extended to include the scalars. The parameters involving the scalars were previously obtained to fit the s-wave [pi][pi] and [pi] K scatterings in the region up to about 1 GeV as well as the strong decay [eta]' --> [eta][pi][pi]. At first, one might expect a large enhancement from diagrams including a light [sigma] (560). However there is an amusing cancellation mechanism which prevents this from occurring. In the simplest model there is an enhancement of about 13 per cent in the [eta] -> 3[pi] decay rate due to the scalars. In a more complicated model which includes derivative type symmetry breakers, the cancellation is modified and the scalars contribute about 30 percent of the total decay r...

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Research paper thumbnail of The Use of High Definition 3D Visualization for Cataract Surgery

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Research paper thumbnail of Lattice 2008 Parallel and Poster Presentations

We present the first result of the baryonic spectral functions at several temperatures above the ... more We present the first result of the baryonic spectral functions at several temperatures above the deconfinement phase transition. The analysis was carried out with the maximum entropy method. We shall discuss the existence of non-trivial structures in the spectral functions and their relation to the diquark and baryonic correlations in the deconfinement phase. 9. Spectrum of closed k-strings in D=2+1 Presenter: Andreas Athenodorou — University of Oxford Time: Friday, 2:30 Room: Tidewater B Section: Vacuum Structure and Confinement Co-authors:

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Research paper thumbnail of Algebraic Multi-Grid Solver For Lattice Qcd On Exascale Hardware: Intel Xeon Phi

In this white paper we describe work done on the development of an efficient iterative solver for... more In this white paper we describe work done on the development of an efficient iterative solver for lattice QCD based on the<br> Algebraic Multi-Grid approach (AMG) within the tmLQCD software suite. This development is aimed at modern computer<br> architectures that will be relevant for the Exa-scale regime, namely multicore processors together with the Intel Xeon Phi coprocessor.<br> Because of the complexity of this solver, implementation turned out to take a considerable effort. Fine tuning and<br> optimization will require more work and will be the subject of further investigation. However, the work presented here<br> provides a necessary initial step in this direction.

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Research paper thumbnail of P o S ( L A T 2 0 0 9 ) 0 3 6 Extending the eigCG algorithm to non-symmetric linear systems with multiple right-hand sides

For Hermitian positive definite linear systems and eigenval ue problems, the eigCG algorithm is a... more For Hermitian positive definite linear systems and eigenval ue problems, the eigCG algorithm is a memory efficient algorithm that solves the linear system and simultaneously computes some of its eigenvalues. The algorithm is based on the Conjugate-Gradi ent (CG) algorithm, however, it uses only a window of the vectors generated by the CG algorithm to c ompute approximate eigenvalues. The number and accuracy of the eigenvectors can be increased by solving more right-hand sides. For Hermitian systems with multiple right-hand sides, the c omputed eigenvectors can be used to speed up the solution of subsequent systems. The algorithm w as tested on Lattice QCD problems by solving the normal equations and was shown to give large sp e d up factors and to remove the critical slowing down as we approach light quark masses. Here, an extension to the nonsymmetric case based on the two-sided Lanczos algorithm is g iven. The new algorithm is tested on Lattice QCD problems and is shown to give ve...

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Research paper thumbnail of Maximal twist and the spectrum of quenched twisted mass lattice QCD

Proceedings of XXIIIrd International Symposium on Lattice Field Theory — PoS(LAT2005)

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Research paper thumbnail of Application of Quadrature Methods for Re-Weighting in Lattice QCD

Proceedings of XXIX International Symposium on Lattice Field Theory — PoS(Lattice 2011)

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Research paper thumbnail of Adaptive method for multicriteria optimization of intensity-modulated proton therapy

Medical Physics, 2018

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The pion form factor from twisted-mass lattice quantum chromodynamics

Canadian Journal of Physics, 2006

The pion form factor offers insight into the transition from perturbative to nonperturbative quan... more The pion form factor offers insight into the transition from perturbative to nonperturbative quantum chromodynamics (QCD), and is of current experimental interest. Twisted-mass lattice QCD is a method for eliminating unphysical zero modes from Wilson lattice simulations; it also allows for removal of the leading lattice spacing artifacts through a momentum-averaging prescription. In our study of the pion form factor, we performed the first explicit computation with momentum averaging in twisted-mass lattice QCD, and the first use of the GMRES-DR algorithm for twisted fermion matrix inversion.PACS No.: 12.38.Gc

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The Scalar Sector and the Eta -\u3e 3 Pi Problem

First, recent work on light scalar mesons, which is of possible interest in connection with the s... more First, recent work on light scalar mesons, which is of possible interest in connection with the strong coupling region of QCD is briefly discussed. Then a very short highlighting of a paper concerned with an application to the eta -\u3e 3 pi problem is presented

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Lattice QCD with a twisted mass term and a strange quark

The European Physical Journal A, 2007

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Research paper thumbnail of Nucleon electromagnetic form factors from twisted mass lattice QCD

Results on the electromagnetic form factors of the nucleon using twisted mass fermion configurati... more Results on the electromagnetic form factors of the nucleon using twisted mass fermion configurations are presented. These include a gauge field ensemble simulated with two degenerate light quarks yielding a pion mass of around 130 MeV, as well as two ensembles that include strange and charm quarks in the sea yielding pion masses of 210 MeV and 373 MeV. Details of the methods used and systematic errors are discussed, such as noise reduction techniques and the effect of excited states contamination.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Improved Seed Methods for Symmetric Positive Definite Linear Equations with Multiple Right-hand Sides

We consider symmetric positive definite systems of linear equations with multiple right-hand side... more We consider symmetric positive definite systems of linear equations with multiple right-hand sides. The seed conjugate gradient method solves one right-hand side with the conjugate gradient method and simultaneously projects over the Krylov subspace thus developed for the other right-hand sides. Then the next system is solved and used to seed the remaining ones. Rounding error in the conjugate gradient method limits how much the seeding can improve convergence. We propose three changes to the seed conjugate gradient method: only the first right-hand side is used for seeding, this system is solved past convergence, and the roundoff error is controlled with some reorthogonalization. We will show that results are actually better with only one seeding, even in the case of related right-hand sides. Controlling rounding error gives the potential for rapid convergence for the second and subsequent right-hand sides.

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Research paper thumbnail of Deflated and restarted symmetric Lanczos methods for eigenvalues and linear equations with multiple right-hand sides

A deflated restarted Lanczos algorithm is given for both solving symmetric linear equations and c... more A deflated restarted Lanczos algorithm is given for both solving symmetric linear equations and computing eigenvalues and eigenvectors. The restarting limits the storage so that finding eigenvectors is practical. Meanwhile, the deflating from the presence of the eigenvectors allows the linear equations to generally have good convergence in spite of the restarting. Some reorthogonalization is necessary to control roundoff error, and several approaches are discussed. The eigenvectors generated while solving the linear equations can be used to help solve systems with multiple right-hand sides. Experiments are given with large matrices from quantum chromodynamics that have many right-hand sides.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Computation of correlation matrices for tetraquark candidates with J^P = 0^+ and flavor structure q_1 q̅_̅2̅ q_3 q̅_3

The conjecture that several recently observed mesons have a structure, which is not dominated by ... more The conjecture that several recently observed mesons have a structure, which is not dominated by an ordinary quark-antiquark pair, but by a four-quark structure, is being actively investigated both theoretical and experimentally. Such a state may be characterized as a mesonic molecule or as a diquark-antidiquark pair. Lattice QCD provides a theoretically sound framework to study such states. To quantitatively investigate the internal structure of such mesons, one needs to precisely compute correlation matrices containing several interpolating operators including two and four quarks. Here we discuss certain technical aspects of such correlation matrices suited to study tetraquark candidates with J^P = 0^+ and flavor structure q_1 q̅_̅2̅ q_3 q̅_3, e.g. the a_0(980) meson, the D_s0^∗ meson and some of the charged c c̅ X states. Some numerical results for the a_0(980) meson are presented.

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Research paper thumbnail of Investigation of light and heavy tetraquark candidates using lattice QCD

We review the status of an ongoing long-term lattice investigation of the spectrum and structure ... more We review the status of an ongoing long-term lattice investigation of the spectrum and structure of tetraquark candidates. We focus on the light scalar meson a_0(980). First steps regarding the study of a possibly existing c c c̅c̅ tetraquark are also outlined.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of THE SCALAR SECTOR AND THE η → 3pi PROBLEM

This Article is brought to you for free and open access by the College of Arts and Sciences at SU... more This Article is brought to you for free and open access by the College of Arts and Sciences at SURFACE. It has been accepted for inclusion in Physics by

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Research paper thumbnail of Problems with Multiple Right-Hand

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Investigation of the tetraquark candidate a0(980): Technical aspects and preliminary results

arXiv: High Energy Physics - Lattice, 2014

We discuss technical aspects and first results of a lattice QCD study of the a0(980) state. We em... more We discuss technical aspects and first results of a lattice QCD study of the a0(980) state. We employ various interpolating operators of quark-antiquark, mesonic molecule, diquark-antidiquark and two-meson type. Both connected and disconnected contributions including diagrams with closed fermion loops are computed. To keep statistical errors small, it is essential to optimize the computation of these diagrams by choosing that combination of techniques most appropriate for each type of diagram from the correlation matrix of interpolating operators. We illustrate, how this can be done, by discussing certain diagrams in detail. We also present preliminary results corresponding to a 4 4 submatrix computed with 2+1 flavors of clover fermions.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The hadron spectrum from twisted mass QCD with a strange quark

arXiv: High Energy Physics - Lattice, 2005

Various suggestions exist for incorporating the strange quark into twisted mass QCD. One option f... more Various suggestions exist for incorporating the strange quark into twisted mass QCD. One option for quenched simulations is to employ two twisted doublets, (u,d) and (c,s), with separate twist angles. Working in the isospin limit, preliminary results for the quenched spectrum of strange hadrons are presented, with both twist angles tuned to pi/2. Splittings within the mass multiplets provide some insight into the symmetry breaking effects of twisted mass lattice QCD.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Effects of Light Scalar Mesons in eta -> 3pi decay

We study the role of a possible nonet of light scalar mesons in the still interesting [eta] ->... more We study the role of a possible nonet of light scalar mesons in the still interesting [eta] -> 3[p]i decay process, with the primary motivation of learning more about the scalars themselves. The framework is a conventional non-linear chiral Lagrangian of pseudoscalars and vectors extended to include the scalars. The parameters involving the scalars were previously obtained to fit the s-wave [pi][pi] and [pi] K scatterings in the region up to about 1 GeV as well as the strong decay [eta]' --> [eta][pi][pi]. At first, one might expect a large enhancement from diagrams including a light [sigma] (560). However there is an amusing cancellation mechanism which prevents this from occurring. In the simplest model there is an enhancement of about 13 per cent in the [eta] -> 3[pi] decay rate due to the scalars. In a more complicated model which includes derivative type symmetry breakers, the cancellation is modified and the scalars contribute about 30 percent of the total decay r...

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Research paper thumbnail of The Use of High Definition 3D Visualization for Cataract Surgery

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Lattice 2008 Parallel and Poster Presentations

We present the first result of the baryonic spectral functions at several temperatures above the ... more We present the first result of the baryonic spectral functions at several temperatures above the deconfinement phase transition. The analysis was carried out with the maximum entropy method. We shall discuss the existence of non-trivial structures in the spectral functions and their relation to the diquark and baryonic correlations in the deconfinement phase. 9. Spectrum of closed k-strings in D=2+1 Presenter: Andreas Athenodorou — University of Oxford Time: Friday, 2:30 Room: Tidewater B Section: Vacuum Structure and Confinement Co-authors:

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Algebraic Multi-Grid Solver For Lattice Qcd On Exascale Hardware: Intel Xeon Phi

In this white paper we describe work done on the development of an efficient iterative solver for... more In this white paper we describe work done on the development of an efficient iterative solver for lattice QCD based on the<br> Algebraic Multi-Grid approach (AMG) within the tmLQCD software suite. This development is aimed at modern computer<br> architectures that will be relevant for the Exa-scale regime, namely multicore processors together with the Intel Xeon Phi coprocessor.<br> Because of the complexity of this solver, implementation turned out to take a considerable effort. Fine tuning and<br> optimization will require more work and will be the subject of further investigation. However, the work presented here<br> provides a necessary initial step in this direction.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of P o S ( L A T 2 0 0 9 ) 0 3 6 Extending the eigCG algorithm to non-symmetric linear systems with multiple right-hand sides

For Hermitian positive definite linear systems and eigenval ue problems, the eigCG algorithm is a... more For Hermitian positive definite linear systems and eigenval ue problems, the eigCG algorithm is a memory efficient algorithm that solves the linear system and simultaneously computes some of its eigenvalues. The algorithm is based on the Conjugate-Gradi ent (CG) algorithm, however, it uses only a window of the vectors generated by the CG algorithm to c ompute approximate eigenvalues. The number and accuracy of the eigenvectors can be increased by solving more right-hand sides. For Hermitian systems with multiple right-hand sides, the c omputed eigenvectors can be used to speed up the solution of subsequent systems. The algorithm w as tested on Lattice QCD problems by solving the normal equations and was shown to give large sp e d up factors and to remove the critical slowing down as we approach light quark masses. Here, an extension to the nonsymmetric case based on the two-sided Lanczos algorithm is g iven. The new algorithm is tested on Lattice QCD problems and is shown to give ve...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Maximal twist and the spectrum of quenched twisted mass lattice QCD

Proceedings of XXIIIrd International Symposium on Lattice Field Theory — PoS(LAT2005)

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Application of Quadrature Methods for Re-Weighting in Lattice QCD

Proceedings of XXIX International Symposium on Lattice Field Theory — PoS(Lattice 2011)

Bookmarks Related papers MentionsView impact