Fock space distributions, structure functions, higher twists, and small x

We compute quark structure functions and the intrinsic Fock space distribution of sea quarks in a hadron wave function at small x. The computation is performed in an effective theory at small x where the gluon field is treated classically. At Q² large compared to an intrinsic scale associated with the density of gluons μ², large compared to the QCD scale Λ_QCD², and large compared to the quark mass squared M², the Fock space distribution of quarks is identical to the distribution function measured in deep inelastic scattering. For Q² ≤M² but Q²≫μ², the quark distribution is computed in terms of the gluon distribution function and explicit expressions are obtained. For Q²≤μ² but Q²≫Λ_QCD² we obtain formal expressions for the quark distribution functions in terms of the glue. An evaluation of these requires a renormalization group analysis of the gluon distribution function in the regime of high parton density. For light quarks at high Q², the DGLAP flavor singlet evolution equations for the parton distributions are recovered. Explicit expressions are given for heavy quark structure functions at small x.