Mario Schröck

Symmetries of hadrons after unbreaking the chiral symmetry

We study hadron correlators upon artificial restoration of the spontaneously broken chiral symmetry. In a dynamical lattice simulation we remove the lowest lying eigenmodes of the Dirac operator from the valence quark propagators and study the evolution of the hadron masses obtained. All mesons and baryons in our study, except for a pion, survive the unbreaking of the chiral symmetry and their exponential decay signals become essentially better. From the analysis of the observed spectroscopic patterns we conclude that confinement still persists while the chiral symmetry is restored. All hadrons fall into different chiral multiplets. The broken

Unbreaking chiral symmetry

U(1{)}_{A}

Coulomb, Landau and maximally Abelian gauge fixing in lattice QCD with multi-GPUs

symmetry does not get restored upon unbreaking the chiral symmetry. We also observe signals of some higher symmetry that includes chiral symmetry as a subgroup. Finally, from comparison of the

The chirally improved quark propagator and restoration of chiral symmetry

\ensuremath{\Delta}\ensuremath{-}N

Enumerating copies in the first Gribov region on the lattice in up to four dimensions

splitting before and after the unbreaking of the chiral symmetry, we conclude that both the color-magnetic and the flavor-spin quark-quark interactions are of equal importance.

Potential energy landscapes for the 2D XY model: Minima, transition states, and pathways

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{sub 1} approach each other) while confining properties persist.

Gauge fixing using overrelaxation and simulated annealing on GPUs

Abstract A lattice gauge theory framework for simulations on graphic processing units (GPUs) using NVIDIA’s CUDA is presented. The code comprises template classes that take care of an optimal data pattern to ensure coalesced reading from device memory to achieve maximum performance. In this work we concentrate on applications for lattice gauge fixing in 3+1 dimensional SU(3) lattice gauge field theories. We employ the overrelaxation, stochastic relaxation and simulated annealing algorithms which are perfectly suited to be accelerated by highly parallel architectures like GPUs. The applications support the Coulomb, Landau and maximally Abelian gauges. Moreover, we explore the evolution of the numerical accuracy of the SU(3) valued degrees of freedom over the runtime of the algorithms in single- (SP) and double-precision (DP). Therefrom we draw conclusions on the reliability of SP and DP simulations and suggest a mixed-precision scheme that performs the critical parts of the algorithm in full DP while retaining 80%–90% of the SP performance. Finally, multi-GPUs are adopted to overcome the memory constraint of single GPUs. A communicator class which hides the MPI data exchange at the boundaries of the lattice domains, via the low bandwidth PCI-Bus, effectively behind calculations in the inner part of the domain is presented. Linear scaling using 16 NVIDIA Tesla C2070 devices and a maximum performance of 3.5 Teraflops on lattices of size down to 64 3 × 256 is demonstrated.

Effects of the low lying Dirac modes on excited hadrons in lattice QCD

The chirally improved (CI) quark propagator in Landau gauge is calculated in two flavor lattice Quantum Chromodynamics. Its wave-function renormalization function Z(p) and mass function M(p) are studied. To minimize lattice artifacts, tree-level improvement of the propagator and treelevel 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) for small momenta is observed.

Propagators in lattice Coulomb gauge and confinement mechanisms

The covariant gauges are known to suffer from the Gribov problem: even after fixing a gauge non-perturbatively, there may still exist residual copies which are physically equivalent to each other, called Gribov copies. While the influence of Gribov copies in the relevant quantities such as gluon propagators has been heavily debated in recent studies, the significance of the role they play in the Faddeev--Popov procedure is hardly doubted. We concentrate on Gribov copies in the first Gribov region, i.e., the space of Gribov copies at which the Faddeev--Popov operator is strictly positive (semi)definite. We investigate compact U(

Effects of the low lying Dirac modes on the spectrum of ground state mesons

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