  We calculate the leading non-analytic quark-mass dependence in the moments of
isovector quark distributions using heavy-baryon chiral perturbation theory.
The results differ from those obtained from the Sullivan process in which hard
scattering occurs through the virtual pion cloud of the nucleon. Our results
provide useful guidance for improving upon the meson-cloud model and can be
used to constrain the extrapolations of the existing lattice QCD results to the
physical quark masses.
