Flavour Distributions in the Nucleons: SU(2) Sea Asymmetry or Isospin   Symmetry Breaking?
  The Gottfried sum rule violation reported by the New Muon Collaboration(NMC) was interpreted as indication for a flavour asymmetry of the sea quark in the nucleons. We investigate the alternative possibility that isospin symmetry between the proton and the neutron is breaking. We examine systematically the consequences of this possibility for several processes, namely, neutrino deep inelastic scattering, charged pion Drell-Yan process, proton Drell-Yan process, and semi-inclusive deep inelastic scattering, and conclude that a decision between the two alternative explanations is possible. 
Bo-Qiang Ma, Andereas Schaefer, and Walter Greiner