Fock space distributions, structure functions, higher twists, and small x - art. no. 094002

We compute quark structure functions and the intrinsic Fock space distribut ion 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 treate d classically, At Q(2) large compared to an intrinsic scale associated with the density of gluons mu(2), large compared to the QCD scale Lambda(QCD)(2 ), and large compared to the quark mass squared M-2, the Fock space distrib ution of quarks is identical to the distribution function measured in deep inelastic scattering. For Q(2) less than or equal to M-2 but Q2 much greate r than mu(2), the quark distribution is computed in terms of the gluon dist ribution function and explicit expressions are obtained. For Q(2) less than or equal to mu(2) but Q(2) much greater than Lambda(QCD)(2) we obtain form al expressions for the quark distribution functions in terms of the glue. A n evaluation of these requires a renormalization group analysis of the gluo n distribution function in the regime of high parton density. For light qua rks at high Q(2), the DGLAP flavor singlet evolution equations for the part on distributions are recovered. Explicit expressions are given for heavy qu ark structure functions at small x. [S0556-2821(99)02305-X].