Alistair Hart

A lattice study of the masses of singlet 0++ mesons

We compute the masses of the flavor singlet 0{sup ++} mesons using (n{sub f}=2) unquenched lattice QCD with the Iwasaki and Wilson gauge actions. Both fermionic and glueball interpolating operators are used to create the states. The mass of the lightest 0{sup ++} meson is suppressed relative to the mass of the 0{sup ++} glueball in quenched QCD at an equivalent lattice spacing. The low value for mass of the lightest flavor singlet 0{sup ++} meson obtained in our calculation could be due to either: that the mass of the meson is much lower than that of the 0{sup ++} glueball in quenched QCD, or due to the effect of lattice artifacts. We present arguments for the first option, but we are unable to rule out the explanation due to lattice artifacts.

OpenMP for accelerators

OpenMP [14] is the dominant programming model for shared-memory parallelism in C, C++ and Fortran due to its easy-touse directive-based style, portability and broad support by compiler vendors. Compute-intensive application regions are increasingly being accelerated using devices such as GPUs and DSPs, and a programming model with similar characteristics is needed here. This paper presents extensions to OpenMP that provide such a programming model. Our results demonstrate that a high-level programming model can provide accelerated performance comparable to that of hand-coded implementations in CUDA.

Index theorem and universality properties of the low-lying eigenvalues of improved staggered quarks

We study various improved staggered quark Dirac operators on quenched gluon backgrounds in lattice QCD generated using a Symanzik-improved gluon action. We find a clear separation of the spectrum into would-be zero modes and others. The number of would-be zero modes depends on the topological charge as expected from the index theorem, and their chirality expectation value is large ( approximately 0.7). The remaining modes have low chirality and show clear signs of clustering into quartets and approaching the random matrix theory predictions for all topological charge sectors. We conclude that improvement of the fermionic and gauge actions moves the staggered quarks closer to the continuum limit where they respond correctly to QCD topology.

Radiative corrections to the lattice gluon action for highly improved staggered quarks and the effect of such corrections on the static potential

We perform a perturbative calculation of the influence of dynamical highly improved staggered quark fermions on the perturbative improvement of the gluonic action in the same way as we have previously done for asqtad fermions. We find the fermionic contributions to the radiative corrections in the Luescher-Weisz gauge action to be somewhat larger for highly improved staggered quark fermions than for asqtad. Using one-loop perturbation theory as a test, we estimate that omission of the fermion-induced radiative corrections in dynamical asqtad simulations will give a measurable effect. The one-loop result gives a systematic shift of about -0.6% in r-circumflex{sub 1} on the coarsest asqtad improved staggered ensembles. This is the correct sign and magnitude to explain the scaling violations seen in {phi}{sub B}=f{sub B}{radical}(M{sub B}) on dynamical lattice ensembles.

Automated generation of lattice QCD Feynman rules

Abstract The derivation of the Feynman rules for lattice perturbation theory from actions and operators is complicated, especially for highly improved actions such as HISQ. This task is, however, both important and particularly suitable for automation. We describe a suite of software to generate and evaluate Feynman rules for a wide range of lattice field theories with gluons and (relativistic and/or heavy) quarks. Our programs are capable of dealing with actions as complicated as (m)NRQCD and HISQ. Automated differentiation methods are used to calculate also the derivatives of Feynman diagrams. Program summary Program title: HiPPY, HPsrc Catalogue identifier: AEDX_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEDX_v1_0.html Program obtainable from: CPC Program Library, Queens University, Belfast, N. Ireland Licensing provisions: GPLv2 (see Additional comments below) No. of lines in distributed program, including test data, etc.: 513 426 No. of bytes in distributed program, including test data, etc.: 4 893 707 Distribution format: tar.gz Programming language: Python, Fortran95 Computer: HiPPy: Single-processor workstations. HPsrc: Single-processor workstations and MPI-enabled multi-processor systems Operating system: HiPPy: Any for which Python v2.5.x is available. HPsrc: Any for which a standards-compliant Fortran95 compiler is available Has the code been vectorised or parallelised?: Yes RAM: Problem specific, typically less than 1 GB for either code Classification: 4.4, 11.5 Nature of problem: Derivation and use of perturbative Feynman rules for complicated lattice QCD actions. Solution method: An automated expansion method implemented in Python (HiPPy) and code to use expansions to generate Feynman rules in Fortran95 (HPsrc). Restrictions: No general restrictions. Specific restrictions are discussed in the text. Additional comments: The HiPPy and HPsrc codes are released under the second version of the GNU General Public Licence (GPL v2). Therefore anyone is free to use or modify the code for their own calculations. As part of the licensing, we ask that any publications including results from the use of this code or of modifications of it cite Refs. [1,2] as well as this paper. Finally, we also ask that details of these publications, as well as of any bugs or required or useful improvements of this core code, would be communicated to us. Running time: Very problem specific, depending on the complexity of the Feynman rules and the number of integration points. Typically between a few minutes and several weeks. The installation tests provided with the program code take only a few seconds to run. References: [1] A. Hart, G.M. von Hippel, R.R. Horgan, L.C. Storoni, Automatically generating Feynman rules for improved lattice eld theories, J. Comput. Phys. 209 (2005) 340–353, doi:10.1016/j.jcp.2005.03.010 , arXiv:hep-lat/0411026 . [2] M. Luscher, P. Weisz, Efficient Numerical Techniques for Perturbative Lattice Gauge Theory Computations, Nucl. Phys. B 266 (1986) 309, doi:10.1016/0550-3213(86)90094-5 .

OpenACC acceleration of the Nek5000 spectral element code

We present a case study of porting NekBone, a skeleton version of the Nek5000 code, to a parallel GPU-accelerated system. Nek5000 is a computational fluid dynamics code based on the spectral element method used for the simulation of incompressible flow. The original NekBone Fortran source code has been used as the base and enhanced by OpenACC directives. The profiling of NekBone provided an assessment of the suitability of the code for GPU systems, and indicated possible kernel optimizations. To port NekBone to GPU systems required little effort and a small number of additional lines of code (approximately one OpenACC directive per 1000 lines of code). The naïve implementation using OpenACC leads to little performance improvement: on a single node, from 16 Gflops obtained with the version without OpenACC, we reached 20 Gflops with the naïve OpenACC implementation. An optimized NekBone version leads to a 43 Gflop performance on a single node. In addition, we ported and optimized NekBone to parallel GPU systems, reaching a parallel efficiency of 79.9% on 1024 GPUs of the Titan XK7 supercomputer at the Oak Ridge National Laboratory.

Moving nonrelativistic QCD for heavy-to-light form factors on the lattice

We formulate nonrelativistic quantum chromodynamics (NRQCD) on a lattice which is boosted relative to the usual discretization frame. Moving NRQCD allows us to treat the momentum for the heavy quark arising from the frame choice exactly. We derive moving NRQCD through

Automatically generating Feynman rules for improved lattice field theories

\mathcal{O}(1/{m}^{2},{v}_{\mathrm{rel}}^{4})

First Experiences Porting a Parallel Application to a Hybrid Supercomputer with OpenMP4.0 Device Constructs

, as accurate as the NRQCD action in present use, both in the continuum and on the lattice with

Rare B decays with moving NRQCD and improved staggered quarks

\mathcal{O}({a}^{4})