Nucleon structure in the chiral regime with domain wall fermions on an improved staggered sea
R. G. Edwards, G. Fleming, Ph. Hagler, J. W. Negele, K. Orginos, A. V. Pochinsky, D. B. Renner, D. G. Richards, W. Schroers
TL;DR
This work uses a mixed-action lattice QCD framework (domain-wall valence quarks on improved-staggered sea) to study nucleon structure in the chiral regime, with pion masses down to about $359\,\mathrm{MeV}$. It reports moments of parton distributions, vector/axial form factors, and generalized parton distributions, applying a self-consistent improved one-loop chiral perturbation theory to extrapolate to the physical point. The results show robust agreement with experimental data for several moments and isovector observables, and reveal detailed spin and orbital angular momentum decompositions via generalized form factors and Ji’s sum rule. The study demonstrates the potential of mixed-action lattice QCD to illuminate the origins of nucleon spin and transverse structure, while outlining future needs such as disconnected contributions and higher-precision, finer-lattice analyses.
Abstract
Moments of unpolarized, helicity, and transversity distributions, electromagnetic form factors, and generalized form factors of the nucleon are presented from a preliminary analysis of lattice results using pion masses down to 359 MeV. The twist two matrix elements are calculated using a mixed action of domain wall valence quarks and asqtad staggered sea quarks and are renormalized perturbatively. Several observables are extrapolated to the physical limit using chiral perturbation theory. Results are compared with experimental moments of quark distributions and electromagnetic form factors and phenomenologically determined generalized form factors, and the implications on the transverse structure and spin content of the nucleon are discussed.