Gauge fixing using overrelaxation and simulated annealing on GPUs

We adopt CUDA-capable Graphic Processing Units (GPUs) for Coulomb, Landau and maximally Abelian gauge fixing in 3+1 dimensional SU(3) lattice gauge field theories. The local overrelaxation algorithm is perfectly suited for highly parallel architectures. Simulated annealing preconditioning strongly increases the probability to reach the global maximum of the gauge functional. We give performance results for single and double precision. To obtain our maximum performance of ~300 GFlops on NVIDIA's GTX 580 a very fine grained degree of parallelism is required due to the register limits of NVIDIA's Fermi GPUs: we use eight threads per lattice site, i.e., one thread per SU(3) matrix that is involved in the computation of a site update.Comment: 7 pages, 2 figures. Talk presented at the 30th International Symposium on Lattice Field Theory, June 24-29, 2012, Cairns, Australi

cuLGT: Lattice Gauge Fixing on GPUs

We adopt CUDA-capable Graphic Processing Units (GPUs) for Landau, Coulomb and maximally Abelian gauge fixing in 3+1 dimensional SU(3) and SU(2) lattice gauge field theories. A combination of simulated annealing and overrelaxation is used to aim for the global maximum of the gauge functional. We use a fine grained degree of parallelism to achieve the maximum performance: instead of the common 1 thread per site strategy we use 4 or 8 threads per lattice site. Here, we report on an improved version of our publicly available code (www.cuLGT.com and github.com/culgt) which again increases performance and is much easier to include in existing code. On the GeForce GTX 580 we achieve up to 470 GFlops (utilizing 80% of the theoretical peak bandwidth) for the Landau overrelaxation code.Comment: 6 pages, 2 figures, code available on cuLGT.com and github.com/culgt, talk presented at GPU Computing in High Energy Physics, September 10-12, 2014, Pisa, Ital

Unbreaking chiral symmetry

In Quantum Chromodynamics (QCD) the eigenmodes of the Dirac operator with small absolute eigenvalues have a close relationship to the dynamical breaking of the chiral symmetry. In a simulation with two dynamical quarks, we study the behavior of meson propagators when removing increasingly more of those modes in the valence sector, thus partially removing effects of chiral symmetry breaking. We find that some of the symmetry aspects are restored (e.g., the masses of $\rho$ and $a_1$ approach each other) while confining properties persist.Comment: 5 pages, 5 figures (figure added, references updated

The chirally improved quark propagator and restoration of chiral symmetry

The chirally improved (CI) quark propagator in Landau gauge is calculated in two flavor lattice Quantum Chromodynamics. Its wave-function renormalization function $Z(p^2)$ and mass function $M(p^2)$ are studied. To minimize lattice artifacts, tree-level improvement of the propagator and tree-level correction of the lattice dressing functions is applied. Subsequently the CI quark propagator under Dirac operator low-mode removal is investigated. The dynamically generated mass in the infrared domain of the mass function is found to dissolve continuously as a function of the reduction level and strong suppression of $Z(p^2)$ for small momenta is observed.Comment: 9 pages, 8 figures; accepted at Phys. Lett.