This review outlines our present experimental knowledge and theoretical understanding of deepinelastic scattering on nuclear targets. The emphasis is primarily on nuclear coherence phenomena, such as shadowing, where the key physics issue is the exploration of hadronic and quark-gluon fluctuations of a high-energy virtual photon and their passage through the nuclear medium. New developments in polarized deep-inelastic scattering on nuclei are also discussed, and more conventional binding and Fermi motion effects are summarized. The report closes with a brief outlook on vector meson electroproduction, nuclear shadowing at very large Q 2 and the physics of high parton densities in QCD.

We present an analysis of twist-2, leading order QCD amplitudes for hard exclusive leptoproduction of mesons in terms of double/nonforward parton distribution functions. After reviewing some general features of nonforward nucleon matrix elements of twist-2 QCD string operators, we propose a phenomenological model for quark and gluon nonforward distribution functions. The corresponding QCD evolution equations are solved in the leading logarithmic approximation for flavor nonsinglet distributions. We derive explicit expressions for hard exclusive π 0 , η, and neutral vector meson production amplitudes and discuss general features of the corresponding cross sections. * Work supported in part by BMBF

We present a unified description of nuclear deep inelastic scattering (DIS) over the whole region 0 < x < 1 of the Bjorken variable. Our approach is based on a relativistically covariant formalism which uses analytical properties of quark correlators. In the laboratory frame it naturally incorporates two mechanisms of DIS: (I) scattering from quarks and antiquarks in the target and (II) production of quark-antiquark pairs followed by interactions with the target. We first calculate structure functions of the free nucleon and develop a model for the quark spectral functions. We show that mechanism (II) is responsible for the sea quark content of the nucleon while mechanism (I) governs the valence part of the nucleon structure functions. We find that the coherent interaction ofqq pairs with nucleons in the nucleus leads to shadowing at small x and discuss this effect in detail. In the large x region DIS takes place mainly on a single nucleon. There we focus on the derivation of the convolution model. We point out that the off-shell properties of the bound nucleon structure function give rise to sizable nuclear effects.

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We study deep-inelastic scattering from polarized nuclei within a covariant framework. A clear connection is established between relativistic and nonrelativistic limits, which enables a rigorous derivation of convolution formulae for the spin-dependent nuclear structure functions g A 1 and g A 2 in terms of offmass-shell extrapolations of polarized nucleon structure functions, g N 1 and g N 2 . Approximate expressions for g A 1,2 are obtained by expanding the offshell g N 1,2 about their on-shell limits. As an application of the formalism we consider nuclear effects in the deuteron, knowledge of which is necessary to obtain accurate information on the spin-dependent structure functions of the neutron.