arXiv subjects

Björn Leder

Publications and source records attributed to Björn Leder.

22 records · Page 2Linked to original sources

arXiv2012

Aggregation-based Multilevel Methods for Lattice QCD

In Lattice QCD computations a substantial amount of work is spent in solving the Dirac equation. In the recent past it has been observed that conventional Krylov solvers tend to critically slow down for large lattices and small quark masses. We present a Schwarz alternating procedure (SAP) multilevel method as a solver for the Clover improved Wilson discretization of the Dirac equation. This approach combines two components (SAP and algebraic multigrid) that have separately been used in lattice QCD before. In combination with a bootstrap setup procedure we show that considerable speed-up over conventional Krylov subspace methods for realistic configurations can be achieved.

hep-lat↗

arXiv2011

Fermions as global correction in lattice QCD

The fermion determinant is a highly non-local object and its logarithm is an extensive quantity. For these reasons it is widely believed that the determinant cannot be treated in acceptance steps of gauge link configurations that differ in a large fraction of the links. However, for exact factorisations of the determinant that separate the ultraviolet from the infra-red modes of the Dirac operator it is known that the latter show less variation under changes of the gauge field compared to the former. Using a factorisation based on recursive domain decomposition allows for a hierarchical algorithm that starts with pure gauge updates of the links within the domains and ends after a number of filters with a global acceptance step. We find that the global acceptance rate is high on moderate lattice sizes. Whether this type of algorithm can help in curing the problem of critical slowing down is presently under study.

hep-lat↗

arXiv2011

Determination of the Static Potential with Dynamical Fermions

We present in detail a technique to extract the potential between a static quark and anti-quark pair from Wilson loops measured on dynamical configurations. This technique is based on HYP smearing and leads to an exponential improvement of the noise-to-signal ratio of Wilson loops. We explain why the correct continuum potential is obtained and show numerical evidence that the cut-off effects are small. We present precise results for the non-perturbative potential. As applications, we determine the scale r_0/a and study the shape of the static potential in the range of distances around r_0, where it can be compared with phenomenological potential models.

hep-lat↗

arXiv2011

Scale r_0 and the static potential from the CLS lattices

We report on the measurement of the static potential and the scale r_0 from HYP-smeared Wilson loops in two flavour QCD. We analyse the quark mass dependence of the potential and r_0 at three lattice spacings. We also compare the QCD static potential around distance r_0 with the static potential obtained from potential models.

hep-lat↗