The Experts below are selected from a list of 35652 Experts worldwide ranked by ideXlab platform
William Detmold - One of the best experts on this subject based on the ideXlab platform.
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machine learning action parameters in lattice Quantum Chromodynamics
Physical Review Letters, 2018Co-Authors: P E Shanahan, Daniel Trewartha, William DetmoldAbstract:Numerical lattice Quantum Chromodynamics studies of the strong interaction are important in many aspects of particle and nuclear physics. Such studies require significant computing resources to undertake. A number of proposed methods promise improved efficiency of lattice calculations, and access to regions of parameter space that are currently computationally intractable, via multi-scale action-matching approaches that necessitate parametric regression of generated lattice datasets. The applicability of machine learning to this regression task is investigated, with deep neural networks found to provide an efficient solution even in cases where approaches such as principal component analysis fail. The high information content and complex symmetries inherent in lattice QCD datasets require custom neural network layers to be introduced and present opportunities for further development.
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baryon baryon interactions and spin flavor symmetry from lattice Quantum Chromodynamics
Physical Review D, 2017Co-Authors: Michael L Wagman, William Detmold, Frank Winter, Emmanuel Chang, Zohreh Davoudi, Kostas Orginos, Martin J Savage, P E ShanahanAbstract:Lattice Quantum Chromodynamics is used to constrain the interactions of two octet baryons at the $SU(3)$ flavor-symmetric point, with quark masses that are heavier than those in nature (equal to that of the physical strange quark mass and corresponding to a pion mass of $\ensuremath{\approx}806\text{ }\text{ }\mathrm{MeV}$). Specifically, the $S$-wave scattering phase shifts of two-baryon systems at low energies are obtained with the application of L\"uscher's formalism, mapping the energy eigenvalues of two interacting baryons in a finite volume to the two-particle scattering amplitudes below the relevant inelastic thresholds. The leading-order low-energy scattering parameters in the two-nucleon systems that were previously obtained at these quark masses are determined with a refined analysis, and the scattering parameters in two other channels containing the $\mathrm{\ensuremath{\Sigma}}$ and $\mathrm{\ensuremath{\Xi}}$ baryons are constrained for the first time. It is found that the values of these parameters are consistent with an approximate $SU(6)$ spin-flavor symmetry in the nuclear and hypernuclear forces that is predicted in the large-${N}_{c}$ limit of QCD. The two distinct $SU(6)$-invariant interactions between two baryons are constrained for the first time at this value of the quark masses, and their values indicate an approximate accidental $SU(16)$ symmetry. The $SU(3)$ irreps containing the $NN({^{1}S}_{0})$, $NN({^{3}S}_{1})$ and $\frac{1}{\sqrt{2}}({\mathrm{\ensuremath{\Xi}}}^{0}n+{\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}p)({^{3}S}_{1})$ channels unambiguously exhibit a single bound state, while the irrep containing the ${\mathrm{\ensuremath{\Sigma}}}^{+}p({^{3}S}_{1})$ channel exhibits a state that is consistent with either a bound state or a scattering state close to threshold. These results are in agreement with the previous conclusions of the NPLQCD collaboration regarding the existence of two-nucleon bound states at this value of the quark masses.
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double β decay matrix elements from lattice Quantum Chromodynamics
Physical Review D, 2017Co-Authors: William Detmold, Brian C Tiburzi, Michael L Wagman, Frank Winter, Emmanuel Chang, Zohreh Davoudi, Kostas Orginos, Martin J Savage, P E ShanahanAbstract:A lattice Quantum Chromodynamics (LQCD) calculation of the nuclear matrix element relevant to the $nn\ensuremath{\rightarrow}ppee{\overline{\ensuremath{\nu}}}_{e}{\overline{\ensuremath{\nu}}}_{e}$ transition is described in detail, expanding on the results presented in Ref. [P. E. Shanahan et al., Phys. Rev. Lett. 119, 062003 (2017)]. This matrix element, which involves two insertions of the weak axial current, is an important input for phenomenological determinations of double-$\ensuremath{\beta}$ decay rates of nuclei. From this exploratory study, performed using unphysical values of the quark masses, the long-distance deuteron-pole contribution to the matrix element is separated from shorter-distance hadronic contributions. This polarizability, which is only accessible in double-weak processes, cannot be constrained from single-$\ensuremath{\beta}$ decay of nuclei, and is found to be smaller than the long-distance contributions in this calculation, but non-negligible. In this work, technical aspects of the LQCD calculations, and of the relevant formalism in the pionless effective field theory, are described. Further calculations of the isotensor axial polarizability, in particular near and at the physical values of the light-quark masses, are required for precise determinations of both two-neutrino and neutrinoless double-$\ensuremath{\beta}$ decay rates in heavy nuclei.
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proton proton fusion and tritium β decay from lattice Quantum Chromodynamics
Physical Review Letters, 2017Co-Authors: Martin J Savage, P E Shanahan, William Detmold, Brian C Tiburzi, Michael L Wagman, Frank Winter, Emmanuel Chang, Zohreh Davoudi, S R Beane, Kostas OrginosAbstract:The nuclear matrix element determining the pp→de^{+}ν fusion cross section and the Gamow-Teller matrix element contributing to tritium β decay are calculated with lattice Quantum Chromodynamics for the first time. Using a new implementation of the background field method, these quantities are calculated at the SU(3) flavor-symmetric value of the quark masses, corresponding to a pion mass of m_{π}∼806 MeV. The Gamow-Teller matrix element in tritium is found to be 0.979(03)(10) at these quark masses, which is within 2σ of the experimental value. Assuming that the short-distance correlated two-nucleon contributions to the matrix element (meson-exchange currents) depend only mildly on the quark masses, as seen for the analogous magnetic interactions, the calculated pp→de^{+}ν transition matrix element leads to a fusion cross section at the physical quark masses that is consistent with its currently accepted value. Moreover, the leading two-nucleon axial counterterm of pionless effective field theory is determined to be L_{1,A}=3.9(0.2)(1.0)(0.4)(0.9) fm^{3} at a renormalization scale set by the physical pion mass, also agreeing within the accepted phenomenological range. This work concretely demonstrates that weak transition amplitudes in few-nucleon systems can be studied directly from the fundamental quark and gluon degrees of freedom and opens the way for subsequent investigations of many important quantities in nuclear physics.
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uncertainty quantification in lattice qcd calculations for nuclear physics
Journal of Physics G, 2015Co-Authors: Silas R Beane, William Detmold, Kostas Orginos, Martin J SavageAbstract:The numerical technique of lattice Quantum Chromodynamics (LQCD) holds the promise of connecting the nuclear forces, nuclei, the spectrum and structure of hadrons, and the properties of matter under extreme conditions with the underlying theory of the strong interactions, Quantum Chromodynamics. A distinguishing, and thus far unique, feature of this formulation is that all of the associated uncertainties, both statistical and systematic can, in principle, be systematically reduced to any desired precision with sufficient computational and human resources. We review the sources of uncertainty inherent in LQCD calculations for nuclear physics, and discuss how each is quantified in current efforts.
Lawrence Meadows - One of the best experts on this subject based on the ideXlab platform.
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mixed precision solver scalable to 16000 mpi processes for lattice Quantum Chromodynamics simulations on the oakforest pacs system
arXiv: Computational Physics, 2017Co-Authors: Taisuke Boku, Yoshinobu Kuramashi, Ken-ichi Ishikawa, Lawrence MeadowsAbstract:Lattice Quantum Chromodynamics (Lattice QCD) is a Quantum field theory on a finite discretized space-time box so as to numerically compute the dynamics of quarks and gluons to explore the nature of subatomic world. Solving the equation of motion of quarks (quark solver) is the most compute-intensive part of the lattice QCD simulations and is one of the legacy HPC applications. We have developed a mixed-precision quark solver for a large Intel Xeon Phi (KNL) system named "Oakforest-PACS", employing the $O(a)$-improved Wilson quarks as the discretized equation of motion. The nested-BiCGSTab algorithm for the solver was implemented and optimized using mixed-precision, communication-computation overlapping with MPI-offloading, SIMD vectorization, and thread stealing techniques. The solver achieved 2.6 PFLOPS in the single-precision part on a $400^3\times 800$ lattice using 16000 MPI processes on 8000 nodes on the system.
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Mixed Precision Solver Scalable to 16000 MPI Processes for Lattice Quantum Chromodynamics Simulations on the Oakforest-PACS System
2017 Fifth International Symposium on Computing and Networking (CANDAR), 2017Co-Authors: Taisuke Boku, Yoshinobu Kuramashi, Ken-ichi Ishikawa, Lawrence MeadowsAbstract:Lattice Quantum Chromodynamics (Lattice QCD) is a Quantum field theory on a finite discretized space-time box so as to numerically compute the dynamics of quarks and gluons to explore the nature of subatomic world. Solving the equation of motion of quarks (quark solver) is the most compute-intensive part of the lattice QCD simulations and is one of the legacy HPC applications. We have developed a mixed-precision quark solver for a large Intel Xeon Phi (KNL) system named "Oakforest-PACS", employing the O(a)-improved Wilson quarks as the discretized equation of motion. The nested-BiCGSTab algorithm for the solver was implemented and optimized using mixed-precision, communication-computation overlapping with MPI-offloading, SIMD vectorization, and thread stealing techniques. The solver achieved 2.6 PFLOPS in the single-precision part on a 400^3 × 800 lattice using 16000 MPI processes on 8000 nodes on the system.
Kostas Orginos - One of the best experts on this subject based on the ideXlab platform.
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baryon baryon interactions and spin flavor symmetry from lattice Quantum Chromodynamics
Physical Review D, 2017Co-Authors: Michael L Wagman, William Detmold, Frank Winter, Emmanuel Chang, Zohreh Davoudi, Kostas Orginos, Martin J Savage, P E ShanahanAbstract:Lattice Quantum Chromodynamics is used to constrain the interactions of two octet baryons at the $SU(3)$ flavor-symmetric point, with quark masses that are heavier than those in nature (equal to that of the physical strange quark mass and corresponding to a pion mass of $\ensuremath{\approx}806\text{ }\text{ }\mathrm{MeV}$). Specifically, the $S$-wave scattering phase shifts of two-baryon systems at low energies are obtained with the application of L\"uscher's formalism, mapping the energy eigenvalues of two interacting baryons in a finite volume to the two-particle scattering amplitudes below the relevant inelastic thresholds. The leading-order low-energy scattering parameters in the two-nucleon systems that were previously obtained at these quark masses are determined with a refined analysis, and the scattering parameters in two other channels containing the $\mathrm{\ensuremath{\Sigma}}$ and $\mathrm{\ensuremath{\Xi}}$ baryons are constrained for the first time. It is found that the values of these parameters are consistent with an approximate $SU(6)$ spin-flavor symmetry in the nuclear and hypernuclear forces that is predicted in the large-${N}_{c}$ limit of QCD. The two distinct $SU(6)$-invariant interactions between two baryons are constrained for the first time at this value of the quark masses, and their values indicate an approximate accidental $SU(16)$ symmetry. The $SU(3)$ irreps containing the $NN({^{1}S}_{0})$, $NN({^{3}S}_{1})$ and $\frac{1}{\sqrt{2}}({\mathrm{\ensuremath{\Xi}}}^{0}n+{\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}p)({^{3}S}_{1})$ channels unambiguously exhibit a single bound state, while the irrep containing the ${\mathrm{\ensuremath{\Sigma}}}^{+}p({^{3}S}_{1})$ channel exhibits a state that is consistent with either a bound state or a scattering state close to threshold. These results are in agreement with the previous conclusions of the NPLQCD collaboration regarding the existence of two-nucleon bound states at this value of the quark masses.
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double β decay matrix elements from lattice Quantum Chromodynamics
Physical Review D, 2017Co-Authors: William Detmold, Brian C Tiburzi, Michael L Wagman, Frank Winter, Emmanuel Chang, Zohreh Davoudi, Kostas Orginos, Martin J Savage, P E ShanahanAbstract:A lattice Quantum Chromodynamics (LQCD) calculation of the nuclear matrix element relevant to the $nn\ensuremath{\rightarrow}ppee{\overline{\ensuremath{\nu}}}_{e}{\overline{\ensuremath{\nu}}}_{e}$ transition is described in detail, expanding on the results presented in Ref. [P. E. Shanahan et al., Phys. Rev. Lett. 119, 062003 (2017)]. This matrix element, which involves two insertions of the weak axial current, is an important input for phenomenological determinations of double-$\ensuremath{\beta}$ decay rates of nuclei. From this exploratory study, performed using unphysical values of the quark masses, the long-distance deuteron-pole contribution to the matrix element is separated from shorter-distance hadronic contributions. This polarizability, which is only accessible in double-weak processes, cannot be constrained from single-$\ensuremath{\beta}$ decay of nuclei, and is found to be smaller than the long-distance contributions in this calculation, but non-negligible. In this work, technical aspects of the LQCD calculations, and of the relevant formalism in the pionless effective field theory, are described. Further calculations of the isotensor axial polarizability, in particular near and at the physical values of the light-quark masses, are required for precise determinations of both two-neutrino and neutrinoless double-$\ensuremath{\beta}$ decay rates in heavy nuclei.
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proton proton fusion and tritium β decay from lattice Quantum Chromodynamics
Physical Review Letters, 2017Co-Authors: Martin J Savage, P E Shanahan, William Detmold, Brian C Tiburzi, Michael L Wagman, Frank Winter, Emmanuel Chang, Zohreh Davoudi, S R Beane, Kostas OrginosAbstract:The nuclear matrix element determining the pp→de^{+}ν fusion cross section and the Gamow-Teller matrix element contributing to tritium β decay are calculated with lattice Quantum Chromodynamics for the first time. Using a new implementation of the background field method, these quantities are calculated at the SU(3) flavor-symmetric value of the quark masses, corresponding to a pion mass of m_{π}∼806 MeV. The Gamow-Teller matrix element in tritium is found to be 0.979(03)(10) at these quark masses, which is within 2σ of the experimental value. Assuming that the short-distance correlated two-nucleon contributions to the matrix element (meson-exchange currents) depend only mildly on the quark masses, as seen for the analogous magnetic interactions, the calculated pp→de^{+}ν transition matrix element leads to a fusion cross section at the physical quark masses that is consistent with its currently accepted value. Moreover, the leading two-nucleon axial counterterm of pionless effective field theory is determined to be L_{1,A}=3.9(0.2)(1.0)(0.4)(0.9) fm^{3} at a renormalization scale set by the physical pion mass, also agreeing within the accepted phenomenological range. This work concretely demonstrates that weak transition amplitudes in few-nucleon systems can be studied directly from the fundamental quark and gluon degrees of freedom and opens the way for subsequent investigations of many important quantities in nuclear physics.
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uncertainty quantification in lattice qcd calculations for nuclear physics
Journal of Physics G, 2015Co-Authors: Silas R Beane, William Detmold, Kostas Orginos, Martin J SavageAbstract:The numerical technique of lattice Quantum Chromodynamics (LQCD) holds the promise of connecting the nuclear forces, nuclei, the spectrum and structure of hadrons, and the properties of matter under extreme conditions with the underlying theory of the strong interactions, Quantum Chromodynamics. A distinguishing, and thus far unique, feature of this formulation is that all of the associated uncertainties, both statistical and systematic can, in principle, be systematically reduced to any desired precision with sufficient computational and human resources. We review the sources of uncertainty inherent in LQCD calculations for nuclear physics, and discuss how each is quantified in current efforts.
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light nuclei and hypernuclei from Quantum Chromodynamics in the limit of su 3 flavor symmetry
Physical Review D, 2013Co-Authors: Silas R Beane, William Detmold, Kostas Orginos, E Chang, Saul D Cohen, Hueywen Lin, Thomas Luu, A ParrenoAbstract:The binding energies of a range of nuclei and hypernuclei with atomic number A 4 and strangeness jsj 2, including the deuteron, di-neutron, H-dibaryon, 3 He, 3 He, 4 He, 4 He, and 4 He, are calculated in the limit of avor-SU(3) symmetry at the physical strange-quark mass with Quantum Chromodynamics (without electromagnetic interactions). The nuclear states are extracted from Lattice QCD calculations performed with nf = 3 dynamical light quarks using an isotropic clover discretization of the quark action in three lattice volumes of spatial extent L 3:4 fm; 4:5 fm and 6:7 fm, and with a single lattice spacing b 0:145 fm.
P E Shanahan - One of the best experts on this subject based on the ideXlab platform.
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machine learning action parameters in lattice Quantum Chromodynamics
Physical Review Letters, 2018Co-Authors: P E Shanahan, Daniel Trewartha, William DetmoldAbstract:Numerical lattice Quantum Chromodynamics studies of the strong interaction are important in many aspects of particle and nuclear physics. Such studies require significant computing resources to undertake. A number of proposed methods promise improved efficiency of lattice calculations, and access to regions of parameter space that are currently computationally intractable, via multi-scale action-matching approaches that necessitate parametric regression of generated lattice datasets. The applicability of machine learning to this regression task is investigated, with deep neural networks found to provide an efficient solution even in cases where approaches such as principal component analysis fail. The high information content and complex symmetries inherent in lattice QCD datasets require custom neural network layers to be introduced and present opportunities for further development.
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baryon baryon interactions and spin flavor symmetry from lattice Quantum Chromodynamics
Physical Review D, 2017Co-Authors: Michael L Wagman, William Detmold, Frank Winter, Emmanuel Chang, Zohreh Davoudi, Kostas Orginos, Martin J Savage, P E ShanahanAbstract:Lattice Quantum Chromodynamics is used to constrain the interactions of two octet baryons at the $SU(3)$ flavor-symmetric point, with quark masses that are heavier than those in nature (equal to that of the physical strange quark mass and corresponding to a pion mass of $\ensuremath{\approx}806\text{ }\text{ }\mathrm{MeV}$). Specifically, the $S$-wave scattering phase shifts of two-baryon systems at low energies are obtained with the application of L\"uscher's formalism, mapping the energy eigenvalues of two interacting baryons in a finite volume to the two-particle scattering amplitudes below the relevant inelastic thresholds. The leading-order low-energy scattering parameters in the two-nucleon systems that were previously obtained at these quark masses are determined with a refined analysis, and the scattering parameters in two other channels containing the $\mathrm{\ensuremath{\Sigma}}$ and $\mathrm{\ensuremath{\Xi}}$ baryons are constrained for the first time. It is found that the values of these parameters are consistent with an approximate $SU(6)$ spin-flavor symmetry in the nuclear and hypernuclear forces that is predicted in the large-${N}_{c}$ limit of QCD. The two distinct $SU(6)$-invariant interactions between two baryons are constrained for the first time at this value of the quark masses, and their values indicate an approximate accidental $SU(16)$ symmetry. The $SU(3)$ irreps containing the $NN({^{1}S}_{0})$, $NN({^{3}S}_{1})$ and $\frac{1}{\sqrt{2}}({\mathrm{\ensuremath{\Xi}}}^{0}n+{\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}p)({^{3}S}_{1})$ channels unambiguously exhibit a single bound state, while the irrep containing the ${\mathrm{\ensuremath{\Sigma}}}^{+}p({^{3}S}_{1})$ channel exhibits a state that is consistent with either a bound state or a scattering state close to threshold. These results are in agreement with the previous conclusions of the NPLQCD collaboration regarding the existence of two-nucleon bound states at this value of the quark masses.
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double β decay matrix elements from lattice Quantum Chromodynamics
Physical Review D, 2017Co-Authors: William Detmold, Brian C Tiburzi, Michael L Wagman, Frank Winter, Emmanuel Chang, Zohreh Davoudi, Kostas Orginos, Martin J Savage, P E ShanahanAbstract:A lattice Quantum Chromodynamics (LQCD) calculation of the nuclear matrix element relevant to the $nn\ensuremath{\rightarrow}ppee{\overline{\ensuremath{\nu}}}_{e}{\overline{\ensuremath{\nu}}}_{e}$ transition is described in detail, expanding on the results presented in Ref. [P. E. Shanahan et al., Phys. Rev. Lett. 119, 062003 (2017)]. This matrix element, which involves two insertions of the weak axial current, is an important input for phenomenological determinations of double-$\ensuremath{\beta}$ decay rates of nuclei. From this exploratory study, performed using unphysical values of the quark masses, the long-distance deuteron-pole contribution to the matrix element is separated from shorter-distance hadronic contributions. This polarizability, which is only accessible in double-weak processes, cannot be constrained from single-$\ensuremath{\beta}$ decay of nuclei, and is found to be smaller than the long-distance contributions in this calculation, but non-negligible. In this work, technical aspects of the LQCD calculations, and of the relevant formalism in the pionless effective field theory, are described. Further calculations of the isotensor axial polarizability, in particular near and at the physical values of the light-quark masses, are required for precise determinations of both two-neutrino and neutrinoless double-$\ensuremath{\beta}$ decay rates in heavy nuclei.
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proton proton fusion and tritium β decay from lattice Quantum Chromodynamics
Physical Review Letters, 2017Co-Authors: Martin J Savage, P E Shanahan, William Detmold, Brian C Tiburzi, Michael L Wagman, Frank Winter, Emmanuel Chang, Zohreh Davoudi, S R Beane, Kostas OrginosAbstract:The nuclear matrix element determining the pp→de^{+}ν fusion cross section and the Gamow-Teller matrix element contributing to tritium β decay are calculated with lattice Quantum Chromodynamics for the first time. Using a new implementation of the background field method, these quantities are calculated at the SU(3) flavor-symmetric value of the quark masses, corresponding to a pion mass of m_{π}∼806 MeV. The Gamow-Teller matrix element in tritium is found to be 0.979(03)(10) at these quark masses, which is within 2σ of the experimental value. Assuming that the short-distance correlated two-nucleon contributions to the matrix element (meson-exchange currents) depend only mildly on the quark masses, as seen for the analogous magnetic interactions, the calculated pp→de^{+}ν transition matrix element leads to a fusion cross section at the physical quark masses that is consistent with its currently accepted value. Moreover, the leading two-nucleon axial counterterm of pionless effective field theory is determined to be L_{1,A}=3.9(0.2)(1.0)(0.4)(0.9) fm^{3} at a renormalization scale set by the physical pion mass, also agreeing within the accepted phenomenological range. This work concretely demonstrates that weak transition amplitudes in few-nucleon systems can be studied directly from the fundamental quark and gluon degrees of freedom and opens the way for subsequent investigations of many important quantities in nuclear physics.
Stanley J Brodsky - One of the best experts on this subject based on the ideXlab platform.
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connecting the hadron mass scale to the fundamental mass scale of Quantum Chromodynamics
Physics Letters B, 2015Co-Authors: Alexandre Deur, Stanley J Brodsky, G F De TeramondAbstract:Abstract Establishing an explicit connection between the long distance physics of confinement and the dynamical interactions of quarks and gluons at short distances has been a long-sought goal of Quantum Chromodynamics. Using holographic QCD, we derive a direct analytic relation between the scale κ which determines the masses of hadrons and the scale Λ s which controls the predictions of perturbative QCD at very short distances. The resulting prediction Λ s = 0.341 ± 0.032 GeV in the MS ‾ scheme agrees well with the experimental average 0.339 ± 0.016 GeV . We also derive a relation between Λ s and the QCD string tension σ. This connection between the fundamental hadronic scale underlying the physics of quark confinement and the perturbative QCD scale controlling hard collisions can be carried out in any renormalization scheme.
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light front Quantum Chromodynamics a framework for the analysis of hadron physics
International Conference on Light-Cone Physics: Hadronic and Particle Physics, 2014Co-Authors: B L G Bakker, Stanley J Brodsky, A Bassetto, W Broniowski, Simon Dalley, T Frederico, Stanislaw D Glazek, John R Hiller, V A Karmanov, D S KulshreshthaAbstract:An outstanding goal of physics is to find solutions that describe hadrons in the theory of strong interactions, Quantum Chromodynamics (QCD). For this goal, the light-front Hamiltonian formulation of QCD (LFQCD) is a complementary approach to the well-established lattice gauge method. LFQCD offers access to the hadrons' nonperturbative quark and gluon amplitudes, which are directly testable in experiments at existing and future facilities. We present an overview of the promises and challenges of LFQCD in the context of unsolved issues in QCD that require broadened and accelerated investigation. We identify specific goals of this approach and address its quantifiable uncertainties. © 2014 Elsevier B.V.
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light front Quantum Chromodynamics a framework for the analysis of hadron physics
arXiv: High Energy Physics - Phenomenology, 2013Co-Authors: B L G Bakker, Stanley J Brodsky, A Bassetto, W Broniowski, Simon Dalley, T Frederico, Stanislaw D Glazek, John R Hiller, V A Karmanov, D S KulshreshthaAbstract:An outstanding goal of physics is to find solutions that describe hadrons in the theory of strong interactions, Quantum Chromodynamics (QCD). For this goal, the light-front Hamiltonian formulation of QCD (LFQCD) is a complementary approach to the well-established lattice gauge method. LFQCD offers access to the hadrons' nonperturbative quark and gluon amplitudes, which are directly testable in experiments at existing and future facilities. We present an overview of the promises and challenges of LFQCD in the context of unsolved issues in QCD that require broadened and accelerated investigation. We identify specific goals of this approach and address its quantifiable uncertainties.
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condensates in Quantum Chromodynamics and the cosmological constant
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Stanley J Brodsky, Robert ShrockAbstract:Casher and Susskind [Casher A, Susskind L (1974) Phys Rev 9:436–460] have noted that in the light-front description, spontaneous chiral symmetry breaking is a property of hadronic wavefunctions and not of the vacuum. Here we show from several physical perspectives that, because of color confinement, quark and gluon condensates in Quantum Chromodynamics (QCD) are associated with the internal dynamics of hadrons. We discuss condensates using condensed matter analogues, the Anti de Sitter/conformal field theory correspondence, and the Bethe–Salpeter–Dyson–Schwinger approach for bound states. Our analysis is in agreement with the Casher and Susskind model and the explicit demonstration of “in-hadron” condensates by Roberts and coworkers [Maris P, Roberts CD, Tandy PC (1998) Phys Lett B 420:267–273], using the Bethe–Salpeter–Dyson–Schwinger formalism for QCD-bound states. These results imply that QCD condensates give zero contribution to the cosmological constant, because all of the gravitational effects of the in-hadron condensates are already included in the normal contribution from hadron masses.
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testing Quantum Chromodynamics with antiprotons
arXiv: High Energy Physics - Phenomenology, 2004Co-Authors: Stanley J BrodskyAbstract:The antiproton storage ring HESR to be constructed at GSI will open up a new range of perturbative and nonperturbative tests of QCD in exclusive and inclusive reactions. I discuss 21 tests of QCD using antiproton beams which can illuminate novel features of QCD. The proposed experiments include the formation of exotic hadrons, measurements of timelike generalized parton distributions, the production of charm at threshold, transversity measurements in Drell-Yan reactions, and searches for single-spin asymmetries. The interactions of antiprotons in nuclear targets will allow tests of exotic nuclear phenomena such as color transparency, hidden color, reduced nuclear amplitudes, and the non-universality of nuclear antishadowing. The AdS/CFT correspondence of large $N_C$ supergravity theory in higher-dimensional anti-de Sitter space with supersymmetric QCD in 4-dimensional space-time has important implications for hadron phenomenology in the conformal limit, including the nonperturbative derivation of counting rules for exclusive processes and the behavior of structure functions at large $x_{bj}.$ String/gauge duality also predicts the QCD power-law fall-off of light-front Fock-state hadronic wavefunctions with arbitrary orbital angular momentum at high momentum transfer. I also review recent work which shows that the diffractive component of deep inelastic scattering, single spin asymmetries, as well as nuclear shadowing and antishadowing, cannot be computed from the LFWFs of hadrons in isolation.
