Effective noise reduction techniques for disconnected loops in Lattice QCD

Abstract

Many Lattice QCD observables of phenomenological interest include so-called all-to-all propagators. The computation of these requires prohibitively large computational resources, unless they are estimated stochastically. This is usually done. However, the computational demand can often be further reduced by one order of magnitude by implementing sophisticated unbiased noise reduction techniques. We combine both well known and novel methods that can be applied to a wide range of problems. We concentrate on calculating disconnected contributions to nucleon structure functions, as one realistic benchmark example. In particular we determine the strangeness contributions to the nucleon, <N|ss|N>, and to the spin of the nucleon, Delta s.

26 pages, 11 figures, v2: table 6, figs 8b and 9b corrected, typos corrected, references updated