Generalized parton distributions can be used to obtain information about the dependence of parton distributions on the impact parameter. Potential consequences for T -odd single-spin asymmetries are discussed.
In this talk, we introduce two sets of twist-3 quark-gluon correlation functions that are relevant to transverse single spin asymmetries, and present corresponding evolution equations at the leading order in strong coupling constant, αs. The similarities and differences between the evolution of the leading power parton distributions and that of the twist-3 multiparton correlation functions are also discussed.