The Light-flavor structure of the nucleon

Recent data on the Gottfried sum and less recent ones on the pion-nucleon sigma term seem to disagree with naive parton-based expectations on the light (i.e., up, down and strange) quark content of the nucleon. We show that these discrepancies are resolved if nonperturbative contributions are included in the analysis of the data. These appear both in the computation of matrix elements of operators, and in their QCD scale dependence, and depend strongly on the quantum numbers of the given state.