We calculate the second moment [Formula: see text] of the flavor-singlet structure function [Formula: see text] for the pion and the kaon in the framework of the QCD sum rule, and investigate how the results depend on their flavor structure (quark contents). Our calculations give similar values of [Formula: see text] for these two mesons as a result of the cancellation among several non-small factors.
Momentum sum rule can be used as an inequality to estimate the lower and upper bounds of the momentum fractions of quarks and gluons in a model of proton valid in a limited x range. We compute such bounds in a self-similarity based model of proton structure function valid in the range 6.2 × 10-7 ≤ x ≤ 10-2. The results conform to the asymptotic QCD expectations.
The combination [Formula: see text] is derived from SLAC data on polarized proton and deuteron targets, evaluated at Q2=10 GeV 2, and compared with the results of SMC experiment. The agreement is satisfactory except for the points at the three lowest x, which have an important role in the SMC evaluation on the L.H.S. of the Bjorken sum rule.