Noise Methods for Flavor Singlet Quantities

Abstract

A discussion of methods for reducing the noise variance of flavor singlet quantities ("disconnected diagrams") in lattice QCD is given. After an introduction, the possible advantage of partitioning the Wilson fermion matrix into disjoint spaces is discussed and a numerical comparison of the variance for three possible partitioning schemes is carried out. The measurement efficiency of lattice operators is examined and shown to be strongly influenced by the Dirac and color partitioning choices. Next, the numerical effects of an automated subtraction algorithm on the noise variance of various disconnected loop matrix elements are examined. It is found that there is a dramatic reduction in the variance of the Wilson point-split electromagnetic currents and that this reduction persists at small quark mass.