We present a new formulation of pseudoscalar meson loop corrections to nucleon parton distributions within a nonlocal covariant chiral effective field theory, including contributions from SU (3) octet and decuplet baryons. The nonlocal Lagrangian, constrained by requirements of local gauge invariance and Lorentz-invariant ultraviolet regularization, generates additional interactions associated with gauge links. We use these to compute the full set of proton → meson + baryon splitting functions, which in general contain on-shell and off-shell contributions, in addition to δ-function terms at zero momentum, along with nonlocal contributions associated with the finite size of the proton. We illustrate the shapes of the various local and nonlocal functions numerically using a simple example of a dipole regulator.

Using recently derived results for one-loop hadronic splitting functions from a nonlocal implementation of chiral effective theory, we study the contributions from pseudoscalar meson loops to flavor asymmetries in the proton. Constraining the parameters of the regulating functions by inclusive production of n, ∆ ++ , Λ and Σ * + baryons in pp collisions, we compute the shape of the light antiquark asymmetryd −ū in the proton and the strange asymmetry s −s in the nucleon sea.With these constraints, the magnitude of thed −ū asymmetry is found to be compatible with that extracted from the Fermilab E866 Drell-Yan measurement, with no indication of a sign change at large values of x, and an integrated value in the range d −ū ≈ 0.09 − 0.17. The s −s asymmetry is predicted to be positive at x > 0, with compensating negative contributions at x = 0, and an integrated x-weighted moment in the range x(s −s) ≈ (0.9 − 2.5) × 10 −3 .

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