Pion cloud and sea quark flavor asymmetry in the impact parameter representation

We study large-distance contributions to the nucleon parton densities in the transverse coordinate (impact parameter) representation based on generalized parton distributions (GPDs). Chiral dynamics generates a distinct component of the partonic structure, located at momentum fractions x≲ M _πM_N and transverse distances b ∼ 1/M _π. We analyze the phenomenological "pion cloud" model of the flavor asymmetry d̄(x)-ū(x) and quantify what fraction of the calculated asymmetry results from the universal large-distance region. We show that in this model the region b > b_core ≈ 0.55 fm (the transverse "quark core" radius estimated from the nucleon's axial charge radius) produces only ∼30% of the asymmetry measured in the FNAL E866 experiment at x ∼01. Our findings indicate that the asymmetry originates mostly from the "quark core" at small transverse distances.