Critical slowing down of lattice QCD simulations

by Dr Stefan Schaefer (Humboldt Universitaet - Institut fuer Physik)

Friday 8 Jan 2010, 10:00 → 11:00 Europe/Zurich

TH Theory Conference Room (CERN)

The algorithmic progress of recent years makes the study of charm quark physics seem within the reach of lattice QCD. A first calculation in 2008, which claimed full control of systematic errors, found a discrepancy to the experimental value of $f_{D_s}$ at the time and speculations about physics beyond the standard model have been made. This talk is about problems of such simulations. For a reliable treatment of charm quarks, fine lattices have to be used. With modern algorithms, however, we observe a very severe critical slowing down as the lattice spacing is decreased, especially in the topological charge. Because of that, simulations of full QCD with a lattice spacing below 0.05fm seem currently out of reach. To better quantify this problem and the influence of various parameters of the simulation, we performed an extensive study in pure gauge theory. We investigated the slowing down in several observables, in particular Wilson loops and the topological charge, and studied the consequences for the estimation of their errors.