Strange quark content of the nucleon

Abstract

We discuss the calculation of disconnected diagrams needed for determining the strange quark content of the nucleon on the lattice. We present results for the strange scalar form factor and the related parameter f T s , which enters into the cross-section for the scattering of dark matter off nuclei in supersymmetric extensions of the standard model. In addition, we present results for the strange contribution to the nucleon's axial and electromagnetic form factors. The calculations were performed with two dynamical flavors of Wilson fermions on a 24 3 × 64 anisotropic lattice with a s ≈ 3a t ≈ 0.11 fm and M π ≈ 400 MeV.

Effective noise reduction techniques for disconnected loops in Lattice QCD

“…Our result on the strangeness contribution to the nucleon spin ∆s ≈ 0 is in agreement with the other recent direct calculation of this quantity [59]. However, we disagree with earlier, less precise studies that employed a summation method over t [60,61,62].…”

Parallelizing the QUDA Library for Multi-GPU Calculations in Lattice Quantum Chromodynamics

“…Until a few years ago, the analysis phase would often account for a relatively small part of the cost of the overall calculation, with analysis corresponding to perhaps 10% of the cost of gauge field generation. In recent years, however, focus has turned to more challenging physical observables and new analysis techniques that demand solutions to the aforementioned linear equations for much larger numbers of right hand sides (see, e.g., [1], [2]). As a result, the relative costs have shifted to the point where analysis often requires an equal or greater amount of computation than gauge field generation.…”

Strangeness and charm content of the nucleon

“…Other recent direct calculations resulted in the values f T s = 0.34(5) for anisotropic n F = 2 Wilson fermions [14] and f T s = 0.015(28) for n F = 2 overlap fermions, fixed to zero topology [13]. An indirect determination with rooted staggered fermions, combining chiral condensate and nucleon two point function data with the Hellmann-Feynman theorem, suggested f T s = 0.063(11) [15].…”

“…Note that this number applies to the lattice scheme and needs to be multiplied by a renormalization factor that we expect to be close to 0.76 for a conversion into the MS scheme. Another recent study yielded ∆s = −0.0064(24) [14], employing n F = 2 anisotropic Wilson fermions. We remark that our value at κ val = κ strange reads −0.0187(54) and, therefore, differs from zero by 3.5 standard deviations.…”