Peter Lepage

Panel discussion on chiral extrapolation of physical observables

This is an approximate reconstruction of the panel discussion on chiral extrapolation of physical observables. The session consisted of brief presentations from panelists, followed by responses from the panel, and concluded with questions and comments from the floor with answers from panelists. In the following, the panelists have summarized their statements, and the ensuing discussion has been approximately reconstructed from notes.

Perturbative improvement for lattice QCD: An Update

Resin-coated filaments wound around a mandrel to make a plastic pipe or fittings. In making a fitting with a nonlinear axis, the mandrel is supported with one end adjacent a winding station and rotated about an axis substantially tangent to the nonlinear axis at the winding station. The rotating mandrel oscillates back and forth past the winding station while maintaining the nonlinear axis substantially tangent to the axis of rotation. Resin-coated filaments pass between longitudinally spaced and curved guide fingers and are wrapped around the rotating mandrel in overlapping helical patterns as it moves back and forth past the winding station. The mandrel is removed from the fitting after the resin has cured.

Further improvements to staggered quarks

Abstract The improved staggered quark action has enabled breakthrough calculations of QCD with three light dynamical quarks. The largest remaining a2 scaling violations come from “taste-changing” interactions, which are significantly reduced over naive quarks because of carefully chosen smearing of the gauge links. Here we examine further improvements to the quark action and show that additional smearing of the links can reduce the taste-changing errors by another factor of two, whilst retaining a fully a2-improved action. The taste-changing errors can be understood within a perturbative calculation of the four-quark operators that appear at one-loop. We also discuss unquenching techniques with such a highly improved action.

The D234 action for light quarks

We investigate a new light fermion action (the “D234” action), which is accurate up to O ( a 3 ) and tadpole-improved O ( a α 3 ) errors. Using D234 with Symanzik- and tadpole-improved glue we find evidence that continuum results for the quenched hadron spectrum (pion, rho and nucleon) can be obtained on coarse lattices.

Improvement and taste symmetry breaking for staggered quarks

We compare several systematically improved actions for staggered quarks, suggested by a perturbative analysis. We study the effect of improvement on the taste changing interactions by calculating the splitting in the pion spectrum.

D semi-leptonic decay form factors with HISQ charm and light quarks

We present a program to study D semi-leptonic decay form factors with HISQ charm and light quarks. In this exploratory work, we study

High precision lattice QCD meets experiment

D_s

Taste changing in staggered quarks

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The Determination of alpha(s) from lattice QCD with 2+1 flavors of dynamical quarks

\eta_s

Precise Determinations of the Decay Constants of B and D mesons

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