Session R9: Lattice QCD in Elementary Particle Physics

Monday, April 14, 2008

I describe recent advances in simulating QCD using the staggered quark action. Current results from the MILC collaboration on the physics of light pseudoscalars (pion and kaon decay constants, $V_{us}$, quark masses, and low energy constants) are presented, as are results from the Fermilab/MILC collaboration on leptonic decay constants and semileptonic form factors of the B and D systems. In addition, I detail the progress that has recently been made in putting staggered QCD simulations on a firmer theoretical footing, in particular by understanding the so-called ``rooting trick'' and the corresponding chiral effective theory.   

Monday, April 14, 2008

Recent advances in both computers and algorithms now allow realistic calculations of Quantum Chromodynamics (QCD) interactions using the numerical technique of lattice QCD. The methods used in so-called ``2+1 flavor" lattice calculations have been verified both by post-dictions of quantities that were already experimentally well- known and by predictions that occurred before the relevant experimental determinations were sufficiently precise. This suggests that the sources of systematic error in lattice calculations are under control, and that lattice QCD can now be reliably used to calculate those weak matrix elements that cannot be measured experimentally but are necessary to interpret the results of many high-energy physics experiments. These same calculations also allow stringent tests of the Standard Model of particle physics, and may therefore lead to the discovery of new physics in the future.   

Monday, April 14, 2008

The quark mass dependence of the computational cost in lattice QCD has proven to be a major obstacle against realistic calculation. I present recent progress in this area, specifically, a new multigrid algorithm which essentially removes this mass dependence.