Radiatively Generated Isospin Violations in the Nucleon

Isospin violating valence and sea distributions are evaluated due to QED leading O(�) corrections to the standard QCD evolution equations. Unique perturbative predictions are obtained within the radiative parton model, and confirm earlier results. Nonperturbative contributions have been estimated and depend on a single free parameter chosen to be the current quark mass. The relevance of our predictions for extracting sin 2 �W from DIS �(¯�)N data (‘NuTeV anomaly’) is discussed as well.