Nucleon and pion PDFs: large-x asymptotics meets functional mimicry

Abstract

We review strategies to unveil the primordial large-xx structure of the nucleons as well as the pion from hard-scattering experiments. Ideas are presented for learning about the x\to 1x→1 limit of nonperturbative QCD dynamics at energy scales of order 1 GeV from collider experiments at much higher scales. The behavior of parton distributions at x\to 1x→1 predicted by the quark counting rules and other low-energy theoretical approaches is contrasted with phenomenological PDFs. Polynomial mimicry of PDF parametrizations is one of many factors that influence the apparent power of the (1-x)(1−x) falloff. We discuss implications of the mimicry for the large-xx falloff of the pion PDFs.