Pion distribution functions from low-order Mellin moments

Abstract

Exploiting an evolution scheme for parton distribution functions (DFs) that is all-orders exact, contemporary lattice-QCD (lQCD) results for low-order Mellin moments of the pion valence quark DF are shown to be mutually consistent. The analysis introduces a means by which key odd moments can be obtained from the even moments in circumstances where only the latter are available. Combining these elements, one arrives at parameter-free lQCD-based predictions for the pointwise behaviour of pion valence, glue, and sea DFs, with sound uncertainty estimates. The behaviour of the pion DFs at large light-front momentum fraction, $x> 0.85$, is found to be consistent with QCD expectations and continuum analyses of pion structure functions, i.e., damping like $(1 -x)^{\beta_{\rm parton}}$, with $\beta_{\rm valence} \approx 2.4$, $\beta_{\rm glue} \approx 3.6$, $\beta_{\rm sea} \approx 4.6$. It may be possible to test these predictions using data from forthcoming experiments.