Gottfried sum rule and the shape ofF 2 ⌍ -F 2 ⌍

The recent experimental determination of the Gottfried sum rule of deep inelastic scattering provides strong evidence that SU(2) flavor symmetry is broken by the sea quark distributions of the nucleon. Two mechanisms have been suggested to explain the data: Pauli blocking and non-perturbative contributions to the sea arising from the pion cloud surrounding the nucleon. We investigate the effects of these two mechanisms on several standard parametrizations of the quark distribution functions and find that each mechanism has different effects on the shapes of these distribution functions. The best agreement between the experimental data and the modified quark distributions occurs when both mechanisms are taken into account using a softπNN form factor and a small Pauli correction.