Chris M. Richards

Methods for pseudoscalar flavor-singlet mesons with staggered fermions

We present the first 2+1 flavor lattice QCD calculations of pseudoscalar flavor-singlet propagators using improved staggered fermions. We explore the relevant techniques and discuss prospects for the larger scale studies now in progress. The disconnected correlator is shown to have a highly non-Gaussian distribution and reliable estimates of the errors require care.

Stout Smearing for Twisted Mass Fermions

≃ O(a). The phase structureis schematically depicted in the left panel of Fig. 1. The phase transition can be observed insimulations with twisted mass fermions, for instance, as a “jump” or even metastabilities in theaverage plaquette value as a function of the hopping parameter (κ). (The right panel of Fig. 1shows thermal cycles to demonstrate this phenomenon.)One possibility to weaken the phase transition and therefore allow for lighter pion masses ata given lattice spacing is to use an improved gauge action like the DBW2, Iwasaki, or tree-levelSymanzik (tlSym) improved gauge action instead of the simple Wilson gauge action. This has beensuccessfully demonstrated in [3, 4, 5].Here we report on our attempts to use a smeared gauge field in th e fermion lattice Diracoperator to further reduce the strength of the phase transition. This is relevant in simulations withN

'Pseudoscalar flavor-singlet physics with staggered fermions'

Accurately calculating the mass of flavor-singlet meson states from numerical lattice simulations is an important milestone for lattice QCD. Careful measurement of the full pseudoscalar flavorsinglet propagator is also a crucial step in understanding the dynamics of the fermion sea on the lattice, in particular for potentially non-trivial formulations such as with 2+1-flavor staggered fermions. We briefly describe details of a dynamical QCD calculation using improved staggered fermions, with 30,000 trajectories, that was run for our studies of flavour singlet mesons.