Gottfried sum rule and the light-flavor content of the nucleon

We discuss the implications for the light-flavor content of the nucleon of the recent experimental results of the New Muon Collaboration (NMC) on the Gottfried sum rule. We perform a phenomenological analysis of the data and of the symmetries of the quark sea in the nucleon. We show that a discrepancy between the data and naive parton model expectations as seen in the NMC data is also indicated by measurements of the nucleon σ term. We compute the isotriplet value of the σ term through the flavor-singlet scale Ward identity, and we use the result to fix the light-flavor content of the nucleon. We discuss the possibility of reproducing the experimental results in various theoretical frameworks, both within effective models of the nucleon and on the basis of perturbative or nonperturbative QCD