On the chiral expansion for parton distributions at small x∼O(mπ2)

In the framework of the chiral perturbation theory (χPT) we computed two- and three-loop corrections to the pion parton distributions which posses δ-function singularities at xBj→0. From this calculation one can conclude that in the region of small xBj∼mπ2/(4πFπ)2 standard χPT needs in the resummation of all orders to get correct description of the PDFs at small-x region. We demonstrate an example of such resummation.