Recent algorithm and machine developments for lattice QCD

Investigations of hadron structure on the lattice

“…1 we see results for the isovector Dirac radius from several different fermion actions. RBC/UKQCD presented an update from the N f = 2 + 1 domain wall fermion run on 24 3 × 64 lattices with a −1 = 1.729 GeV [12] (red circles), while LHPC updated their mixed action (DWF valence, asqtad sea) results at their lightest pion masses [13] (green right triangles). Additionally, LHPC have started running on the 32 3 × 64 DWF configurations with a −1 ≈ 2.4 GeV generated by the RBC/UKQCD collaborations, and preliminary results from these runs are shown by the black upside-down triangles [13].…”

“…Using their results at the smallest 3 values of Q 2 , the authors computed the pion charge radius and, using the NLO expression from ChPT [32] 3) and the value of the pion decay constant in the chiral limit [33], are able to determine the LEC, l r 6 (m ρ ) = −0.0093 (10). Evaluting the expression using the physical m π gives r 2 π = 0.418(28) fm 2 , compared with r 2 π exp = 0.452(11) fm 2 .…”

“…They perform a test with quenched lattices for two different spatial volumes ((1.6 fm) 3 and (2.4 fm) 3 ), they implement a "patch" to the field by adding the x-link modification A µ (L−1, y, z,t) = −aBLyδ µx if x = L − 1, resulting a field that is quantised in units of 2π/L 2 . They find that when using unpatched data with qa 2 B < 2π/L, large finite size effects are seen on the small volume.…”

“…This is one of the main motivations of the 12 GeV Jefferson Lab upgrade which aims to [2]: search for exotic mesons; study the role of hidden flavours in the nucleon; map out the spin and flavour dependence of the valence parton distribution functions; explore nuclear medium effecs; and measure the generalised parton distribution functions of the nucleon. It is imperative that these and other exciting experimental efforts, such as those at COMPASS/CERN and FAIR/GSI, are matched by modern lattice simulations which, thanks to recent innovative computer and algorithmic improvements [3], are now capable of reaching light quark masses (m π < 300 MeV) and large volumes (>3 fm) [4].…”

Hadronic structure from lattice QCD

“…This means that in order to compare with or provide predictions for experiment, we need to extrapolate the lattice results to the infinite volume and continuum limits, and the physical quark masses. This is an extremely difficult task, but with the advent of new computers, significant progress is now being made in getting these systematics under control [1].…”