Small- and large-x nucleon spin structure from a global QCD analysis of polarized parton distribution functions

I investigate the behavior of spin-dependent parton distribution functions in the regions of small and large momentum fractions x. I present a systematic comparison between predictions for relevant observables obtained with various models of nucleon spin structure and a recent global analysis of spin-dependent distributions, NNPDFpol1.1. Together with its unpolarized counterpart, NNPDF2.3, they form a mutually consistent set of parton distributions. Because they include most of the available experimental information, and are determined with a minimally biased methodology, these are especially suited for such a study. I show how NNPDFpol1.1 can discriminate between different theoretical models, even though NNPDF uncertainties remain large near the endpoints x→0 and x→1, due to the lack of experimental information. I discuss how our knowledge of nucleon spin structure may be improved at small x by future measurements at an Electron–Ion Collider, and at large x by recent measurements at Jefferson Lab, also in view of its 12 GeV upgrade. Keywords: Parton distribution functions (PDFs), Polarized nucleon structure, Regge theory, Hadron model