We present a novel technique for the determination of the topological susceptibility (related to the variance of the distribution of global topological charge) from lattice gauge theory simulations, based on maximum-likelihood analysis of the Markov-
chain Monte Carlo time series. This technique is expected to be particularly useful in situations where relatively few tunneling events are observed. Restriction to a lattice subvolume on which topological charge is not quantized is explored, and may lead to further improvement when the global topology is poorly sampled. We test our proposed method on a set of lattice data, and compare it to traditional methods.
We describe a method to construct irreducible baryon operators using all-to-all quark propagators. It was demonstrated earlier that a large basis of extended baryon operators on anisotropic, quenched lattices can be used to reliably extract the masse
s of 5 or more excited states in the nucleon channel. All-to-all quark propagators are expected to be needed when studying these excited states on light, dynamical configurations because contributions from multi-particle states are expected to be significant. The dilution method is used to approximate the all-to-all quark propagators. Low-lying eigenmodes can also be used if necessary. For efficient computation of matrix elements of the interpolating operators, the algorithms should exploit the fact that many extended baryon operators can be obtained from the different linear combinations of three-quark colour-singlet operators. The sparseness of the diluted noise vectors also afford several computation simplifications. Some preliminary results are presented for nucleon effective masses.
The issues involved in a determination of the baryon resonance spectrum in lattice QCD are discussed. The variational method is introduced and the need to construct a sufficient basis of interpolating operators is emphasised. The construction of bary
on operators using group-theory techniques is outlined. We find that the use both of quark-field smearing and link-field smearing in the operators is essential firstly to reduce the coupling of operators to high-frequency modes and secondly to reduce the gauge-field fluctuations in correlators. We conclude with a status report of our current investigation of baryon spectroscopy.
The nucleon axial charge is calculated as a function of the pion mass in full QCD. Using domain wall valence quarks and improved staggered sea quarks, we present the first calculation with pion masses as light as 354 MeV and volumes as large as (3.5
fm)^3. We show that finite volume effects are small for our volumes and that a constrained fit based on finite volume chiral perturbation theory agrees with experiment within 7% statistical errors.
The design and implementation of large sets of spatially-extended, gauge-invariant operators for use in determining the spectrum of baryons in lattice QCD computations are described. Group-theoretical projections onto the irreducible representations
of the symmetry group of a cubic spatial lattice are used in all isospin channels. The operators are constructed to maximize overlaps with the low-lying states of interest, while minimizing the number of sources needed in computing the required quark propagators. Issues related to the identification of the spin quantum numbers of the states in the continuum limit are addressed.
We report on progress and future plans for calculating kaon weak matrix elements for epsilon/epsilon using staggered fermions.
We present preliminary results of matrix elements of four-fermion operators relevant to the determination of e and e/e using staggered fermions.
