Publications (19)29.03 Total impact
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ABSTRACT: This is the report of the Computing Frontier working group on Lattice Field Theory prepared for the proceedings of the 2013 Community Summer Study ("Snowmass"). We present the future computing needs and plans of the U.S. lattice gauge theory community and argue that continued support of the U.S. (and worldwide) latticeQCD effort is essential to fully capitalize on the enormous investment in the highenergy physics experimental program. We first summarize the dramatic progress of numerical latticeQCD simulations in the past decade, with some emphasis on calculations carried out under the auspices of the U.S. LatticeQCD Collaboration, and describe a broad program of latticeQCD calculations that will be relevant for future experiments at the intensity and energy frontiers. We then present details of the computational hardware and software resources needed to undertake these calculations.10/2013;  [Show abstract] [Hide abstract]
ABSTRACT: Quantum chromodynamics (QCD) is the widely accepted theory of the strong interactions of quarks and gluons. Only through large scale numerical simulation has it been possible to work out the predictions of this theory for a vast range of phenomena relevant to the US Department of Energy experimental program. Such simulations are essential to support the discovery of new phenomena and more fundamental interactions. With support from SciDAC the USQCD collaboration has developed software and prototyped custom computer hardware to carry out the required numerical simulations. We have developed a robust, portable dataparallel code suite. It provides a userfriendly basis for writing physics application codes for carrying out the calculations needed to predict the phenomenology of QCD. We are using this efficient and optimized code base to develop new physics application code, to improve the performance of legacy code, and to construct higher level tools, such as QCDspecific sparse matrix solvers. We give a brief overview of the design of the data parallel API and its various components. We describe performance gains achieved in the past year. Finally, we present plans for further improvements under SciDAC2.Journal of Physics Conference Series 09/2006;  [Show abstract] [Hide abstract]
ABSTRACT: Dtheory is an alternative nonperturbative approach to quantum field theory formulated in terms of discrete quantized variables instead of classical fields. Classical scalar fields are replaced by generalized quantum spins and classical gauge fields are replaced by quantum links. The classical fields of a ddimensional quantum field theory reappear as lowenergy effective degrees of freedom of the discrete variables, provided the (d+1)dimensional Dtheory is massless. When the extent of the extra Euclidean dimension becomes small in units of the correlation length, an ordinary ddimensional quantum field theory emerges by dimensional reduction. The Dtheory formulation of scalar field theories with various global symmetries and of gauge theories with various gauge groups is constructed explicitly and the mechanism of dimensional reduction is investigated.Nuclear Physics B 08/2004; · 3.95 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We describe the construction of large scale clusters for lattice QCD computing being developed under the umbrella of the U.S. DoE SciDAC initiative. We discuss the study of floating point and network performance that drove the design of the cluster, and present our plans for future multiTerascale facilities.Nuclear Physics B  Proceedings Supplements 05/2003; 119:10441046. · 0.88 Impact Factor 
Article: QCD at fixed topology
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ABSTRACT: Since present Monte Carlo algorithms for lattice QCD may become trapped in a fixed topological charge sector, it is important to understand the effect of calculating at fixed topology. In this Letter, we show that although the restriction to a fixed topological sector becomes irrelevant in the infinite volume limit, it gives rise to characteristic finitesize effects due to contributions from all θvacua. We calculate these effects and show how to extract physical results from numerical data obtained at fixed topology.Physics Letters B 03/2003; · 6.02 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Moments of light cone quark density, helicity, and transversity distributions are calculated in unquenched lattice QCD at β = 5.5 and β = 5.3 using Wilson fermions on 163 x 32 lattices. These results are combined with earlier calculations at β = 5.6 using SESAM configurations to study the continuum limit.Nuclear Physics B  Proceedings Supplements 12/2002; · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The fomalism is developed to express nucleon matrix elements of the electromagnetic current in terms of form factors consistent with the translational, rotational, and parity symmetries of a cubic lattice. We calculate the number of these form factors and show how appropriate linear combinations approach the continuum limit.Nuclear Physics B  Proceedings Supplements 12/2002; · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Because present Monte Carlo algorithms for lattice QCD may become trapped in a given topological charge sector when one approaches the continuum limit, it is important to understand the effect of calculating at fixed topology. In this work, we show that although the restriction to a fixed topological sector becomes irrelevant in the infinite volume limit, it gives rise to characteristic finite size effects due to contributions from all θvacua. We calculate these effects and show how to extract physical results from numerical data obtained at fixed topology.Nuclear Physics B  Proceedings Supplements 03/2002; · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Moments of the quark density, helicity, and transversity distributions are calculated in unquenched lattice QCD. Calculations of proton matrix elements of operators corresponding to these moments through the operator product expansion have been performed on $16^3 \times 32$ lattices for Wilson fermions at $\beta = 5.6$ using configurations from the SESAM collaboration and at $\beta = 5.5$ using configurations from SCRI. Oneloop perturbative renormalization corrections are included. At quark masses accessible in present calculations, there is no statistically significant difference between quenched and full QCD results, indicating that the contributions of quarkantiquark excitations from the Dirac Sea are small. Close agreement between calculations with cooled configurations containing essentially only instantons and the full gluon configurations indicates that quark zero modes associated with instantons play a dominant role. Naive linear extrapolation of the full QCD calculation to the physical pion mass yields results inconsistent with experiment. Extrapolation to the chiral limit including the physics of the pion cloud can resolve this discrepancy and the requirements for a definitive chiral extrapolation are described.Physical review D: Particles and fields 03/2002;  [Show abstract] [Hide abstract]
ABSTRACT: Quantum link models are a novel formulation of gauge theories in terms of discrete degrees of freedom. These degrees of freedom are described by quantum operators acting in a finitedimensional Hilbert space. We show that for certain representations of the operator algebra, the usual YangMills action is recovered in the continuum limit. The quantum operators can be expressed as bilinears of fermionic creation and annihilation operators called rishons. Using the rishon representation the quantum link Hamiltonian can be expressed entirely in terms of colorneutral operators. This allows us to study the large N_c limit of this model. In the 't Hooft limit we find an area law for the Wilson loop and a mass gap. Furthermore, the strong coupling expansion is a topological expansion in which graphs with handles and boundaries are suppressed. Comment: Lattice2001(theorydevelop), poster by O. Baer and talk by B. Schlittgen, 6 pagesNuclear Physics B  Proceedings Supplements 10/2001; · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Moments of the quark density distribution, moments of the quark helicity distribution, and the tensor charge are calculated in full QCD. Calculations of matrix elements of operators from the operator product expansion have been performed on $16^3 \times 32$ lattices for Wilson fermions at $\beta = 5.6$ using configurations from the SESAM collaboration and at $\beta = 5.5$ using configurations from SCRI. Oneloop perturbative renormalization corrections are included. Selected results are compared with corresponding quenched calculations and with calculations using cooled configurations.Nuclear Physics B  Proceedings Supplements 12/2000; · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We show that cluster algorithms for quantum models have a meaning independent of the basis chosen to construct them. Using this idea, we propose a new method for measuring with little effort a whole class of Green’s functions, once a cluster algorithm for the partition function has been constructed. To explain the idea, we consider the quantum XY model and compute its two point Green’s function in various ways, showing that all of them are equivalent. We also provide numerical evidence confirming the analytic arguments. Similar techniques are applicable to other models. In particular, in the recently constructed quantum link models, the new technique allows us to construct improved estimators for Wilson loops and may lead to a very precise determination of the glueball spectrum.Physica A: Statistical Mechanics and its Applications 12/1998; 261(3):520533. · 1.72 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Instantons are the natural mechanism in nonperturbative QCD to remove helicity from valence quarks and transfer it to gluons and quarkantiquark pairs. To understand the extent to which instantons explain the socalled “spin crisis” in the nucleon, we calculate moments of spindependent structure functions in quenched QCD and compare them with the results obtained with cooled configurations from which essentially all gluon contributions except instantons have been removed. Preliminary results are presented.Nuclear Physics B  Proceedings Supplements 10/1998; · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We evaluate a perfect quarkgluon vertex function for QCD in coordinate space and truncate it to a short range. We present preliminary results for the charmonium spectrum using this quasiperfect action.Nuclear Physics B  Proceedings Supplements 04/1998; · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We show that cluster algorithms for quantum models have a meaning independent of the basis chosen to construct them. Using this idea, we propose a new method for measuring with little effort a whole class of Green’s functions, once a cluster algorithm for the partition function has been constructed. To explain the idea, we consider the quantum XY model and compute its two point Green’s function in various ways, showing that all of them are equivalent. We also provide numerical evidence confirming the analytic arguments. Similar techniques are applicable to other models. In particular, in the recently constructed quantum link models, the new technique allows us to construct improved estimators for Wilson loops and may lead to a very precise determination of the glueball spectrum.Physica A: Statistical Mechanics and its Applications 02/1998; · 1.72 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Lattice actions and topological charges that are classically and quantum mechanically perfect (i.e. free of lattice artifacts) are constructed analytically for the quantum rotor. It is demonstrated that the Manton action is classically perfect while the Villain action is quantum perfect. The geometric construction for the topological charge is only perfect at the classical level. The quantum perfect lattice topology associates a topological charge distribution, not just a single charge, with each lattice field configuration. For the quantum rotor with the classically perfect action and topological charge, the remaining cutoff effects are exponentially suppressed. Comment: 12 pages, including two figures. ordinary LaTeX, requires fps.sty; Submitted to Phys. Lett. BPhysics Letters B 04/1997; · 6.02 Impact Factor 
Article: QCD as a Quantum Link Model
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ABSTRACT: QCD is constructed as a lattice gauge theory in which the elements of the link matrices are represented by noncommuting operators acting in a Hilbert space. The resulting quantum link model for QCD is formulated with a fifth Euclidean dimension, whose extent resembles the inverse gauge coupling of the resulting fourdimensional theory after dimensional reduction. The inclusion of quarks is natural in Shamir's variant of Kaplan's fermion method, which does not require finetuning to approach the chiral limit. A rishon representation in terms of fermionic constituents of the gluons is derived and the quantum link Hamiltonian for QCD with a U(N) gauge symmetry is expressed in terms of glueball, meson and constituent quark operators. The new formulation of QCD is promising both from an analytic and from a computational point of view. Comment: 27 pages, including three figures. ordinary LaTeX; Submitted to Nucl. Phys. BPhysical review D: Particles and fields 04/1997;  [Show abstract] [Hide abstract]
ABSTRACT: We describe a number of aspects in our attempt to construct an approximately perfect lattice action for QCD. Free quarks are made optimally local on the whole renormalized trajectory and their couplings are then truncated by imposing 3periodicity. The spectra of these short ranged fermions are excellent approximations to continuum spectra. The same is true for free gluons. We evaluate the corresponding perfect quarkgluon vertex function, identifying in particular the ``perfect clover term''. First simulations for heavy quarks show that the mass is strongly renormalized, but again the renormalized theory agrees very well with continuum physics. Furthermore we describe the multigrid formulation for the nonperturbative perfect action and we present the concept of an exactly (quantum) perfect topological charge on the lattice. Comment: 14 pages, 17 figures, Talk presented at LATTICE96(improvement)Nuclear Physics B  Proceedings Supplements 08/1996; · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We consider a particular 4 state spin system composed of two Ising spins (~$s_x, \; \sigma_x$~) with independent hopping parameters $\kappa_1, \kappa_2$, coupled by a bilinear Yukawa term, $y s_x \sigma_x$. The Yukawa term is solely responsible for breaking the global $ Z_2 \times Z_2$ symmetry down to $Z_2$. This model is intended as an illustration of general coupled Higgs system where scalars can arise both as composite and elementary excitations. For the Ising example in 2d, we give convincing numerical evidence of the universality of the two spin system with the one spin Ising model, by Monte Carlo simulations and finite scaling analysis . We also show that as we approach the phase transition, universality arises by a separation of low mass spin waves from an extra set of spin waves with an energy gap that diverges as the correlations length divergesPhysica A: Statistical Mechanics and its Applications 08/1995; · 1.72 Impact Factor
Publication Stats
394  Citations  
29.03  Total Impact Points  
Top Journals
Institutions

1995–2006

Boston University
 Department of Physics
Boston, MA, United States


2000

Massachusetts Institute of Technology
 Center for Theoretical Physics
Cambridge, Massachusetts, United States
