The four articles of the present volume address very different topics in nuclear physics and, indeed, encompass experiments at very different kinds of exp- imental facilities. The range of interest of the articles extends from the nature of the substructure of the nucleon and the deuteron to the general properties of the nucleus, including its phase transitions and its rich and unexpected quantal properties. The first article by Fillipone and Ji reviews the present experimental and theoretical situation pertaining to our knowledge of the origin of the spin of the nucleon. Until about 20 years ago the half-integral spin of the neutron and p- ton was regarded as their intrinsic property as Dirac particles which were the basic building blocks of atomic nuclei. Then, with the advent of the Standard Model and of quarks as the basic building blocks, the substructure of the - cleon became the subject of intense interest. Initial nonrelativistic quark m- els assigned the origin of nucleon spin to the fundamental half-integral spin of its three constituent quarks, leaving no room for contributions to the spin from the gluons associated with the interacting quarks or from the orbital angular momentum of either gluons or quarks. That naive understanding was shaken, about fifteen years ago, by experiments involving deep-inelastic scattering of electrons or muons from nucleons.

Multi-Quark Systems in Hadronic Physics; Bakker, Narodetskii. The Third Generation of Nuclear Physics with the Microscopic Cluster Model; Larganke. The Fermion Dynamical Symmetry Model; Wu, et al. Index.

The three articles of the present volume pertain to very different subjects, all ofconsiderable current interest. The first reviews the fascinating history ofthe search for nucleon substructure in the nucleus using the strength ofGamow- Teller excitations. The second deals with deep inelastic lepton scattering as a probe ofthe non-perturbative structure of the nucleon. The third describes the present state ofaffairs for muon catalyzed fusion, an application of nuclear physics which many new experiments have helped to elucidate. This volume certainly illustrates the broad range ofphysics within our field. The article on Nucleon Charge-Exchange Reactions at Intermediate Energy, by Parker Alford and Brian Spicer, reviews recent data which has clarified one of the greatest puzzles of nuclear physics during the past two decades, namely, the "missing strength" in Gamow-Teller (GT) transitions. The nucleon-nucleon interaction contains a GT component which has a low-lying giant resonance. The integrated GT strength is subject to a GT sum rule. Early experiments with (n, p) charge exchange reactions found only about half of the strength, required by the sum rule, in the vicinity of the giant resonance. At the time, new theoretical ideas suggested that the GT strength was especially sensitive to renormalization from effects pertaining to nucleon substructure, particularly the delta excitation of the nucleon in the nucleus.

This volume presents five pedagogical articles spanning frontier developments in contemporary nuclear physics ranging from the physics of a single nucleon to nucleosynthesis in the Big Bang. Although the objectives of Advances in Nuclear Physics have been and will continue to be quite distinct from those of conventional conference proceedings, the articles in this volume are carefully edited and expanded manuscripts based on an outstanding series of lectures delivered at the VI J. A. Swieca Summer School in Brazil. Starting at the smallest scale, the first article by Dan Olof Riska addresses realistic chiral symmetric models of the nucleon. Since the analytic tools are not yet developed to solve nonperturbative QCD directly, significant effort has been devoted in recent years to the development of models which incorporate and are constrained by the approximate chiral symmetry manifested in QCD. This article provides a clear introduction to chiral symmetry and the Skyrme model, and discusses the Skyrme model's relation to the chiral bag model, its extensions, and its application to nucleons and hyperons.

For the first half of the 20th Century, low-energy nuclear physics was one of the dominant foci of all of science. Then accelerators prospered and energies rose, leading to an increase of interest in the GeV regime and beyond. The three articles comprising this end-of-century Advances in Nuclear Physics present a fitting and masterful summary of the energy regimes through which nuclear physics has developed and promises to develop in future. One article describes new information about fundamental symmetries found with kV neutrons. Another reviews our progress in understanding nucleon-nucleus scattering up to 1 GeV. The third analyzes dilepton production as a probe for quark-gluon plasmas generated in relativistic heavy-ion collisions.

This volume of Advances in Nuclear Physics addresses two very different frontiers of contemporary nuclear physics - one highly theoretical and the other solidly phenomenological. The first article by Matthias Burkardt provides a pedagogical overview of the timely topic of light front quantization. Although introduced decades ago by Dirac, light front quantization has been a central focus in theoretical - clear and particle physics in recent years for two majorreasons. The first, as discussed in detail by Burkardt, is that light-cone coordinates are the natural coordinates for describing high-energy scattering. The wealth of data in recent years on nucleon and nucleus structure functions from high-energy lepton and hadron scattering thus provides a strong impetus for understanding QCD on the light cone. Second, as theorists have explored light front quantization, a host of deep and intriguing theoretical questions have arisen associated with the triviality of the vacuum, the role of zero modes, rotational invariance, and renormalization. These issues are so compelling that they are now intensively investigated on their own merit, independent of the particular application to high-energy scattering. This article provides an excellent introduction and overview of the motivation from high-energy scattering, an accessible - scription of the basic ideas, an insightful discussion of the open problems, and a helpful guide to the specialized literature. It is an ideal opportunity for those with a spectator's acquaintance to develop a deeper understanding of this important field.

This volume contains two major articles, one providing a historical retrosp- tive of one of the great triumphs of nuclear physics in the twentieth century and the other providing a didactic introduction to one of the quantitative tools for understanding strong interactions in the twenty-first century. The article by Igal Talmi on "Fifty Years of the Shell Model - the Quest for the Effective Interaction," pertains to a model that has dominated nuclear physics since its infancy and that developed with astonishing results over the next five decades. Talmi is uniquely positioned to trace the history of the Shell Model. He was active in developing the ideas at the shell model's inception, he has been central in most of the subsequent initiatives which expanded, cl- ified and applied the shell model and he has remained active in the field to the present time. Wisely, he has chosen to restrict his review to the domin- ing issue: the choice of the effective interactions among valence nucleons that determine the properties of low lying nuclear energy levels. The treatment of the subject is both bold and novel for our series. The ideas pertaining to the effective interaction for the shell model are elucidated in a historical sequence.

For the first half of the 20th Century, low-energy nuclear physics was one of the dominant foci of all of science. Then accelerators prospered and energies rose, leading to an increase of interest in the GeV regime and beyond. The three articles comprising this end-of-century Advances in Nuclear Physics present a fitting and masterful summary of the energy regimes through which nuclear physics has developed and promises to develop in future. One article describes new information about fundamental symmetries found with kV neutrons. Another reviews our progress in understanding nucleon-nucleus scattering up to 1 GeV. The third analyzes dilepton production as a probe for quark-gluon plasmas generated in relativistic heavy-ion collisions.

This volume contains two major articles, one providing a historical retrosp- tive of one of the great triumphs of nuclear physics in the twentieth century and the other providing a didactic introduction to one of the quantitative tools for understanding strong interactions in the twenty-first century. The article by Igal Talmi on "Fifty Years of the Shell Model - the Quest for the Effective Interaction", pertains to a model that has dominated nuclear physics since its infancy and that developed with astonishing results over the next five decades. Talmi is uniquely positioned to trace the history of the Shell Model. He was active in developing the ideas at the shell model's inception, he has been central in most of the subsequent initiatives which expanded, cl- ified and applied the shell model and he has remained active in the field to the present time. Wisely, he has chosen to restrict his review to the domin- ing issue: the choice of the effective interactions among valence nucleons that determine the properties of low lying nuclear energy levels. The treatment of the subject is both bold and novel for our series. The ideas pertaining to the effective interaction for the shell model are elucidated in a historical sequence.

This volume presents five pedagogical articles spanning frontier developments in contemporary nuclear physics ranging from the physics of a single nucleon to nucleosynthesis in the Big Bang. Although the objectives of Advances in Nuclear Physics have been and will continue to be quite distinct from those of conventional conference proceedings, the articles in this volume are carefully edited and expanded manuscripts based on an outstanding series of lectures delivered at the VI J. A. Swieca Summer School in Brazil. Starting at the smallest scale, the first article by Dan Olof Riska addresses realistic chiral symmetric models of the nucleon. Since the analytic tools are not yet developed to solve nonperturbative QCD directly, significant effort has been devoted in recent years to the development of models which incorporate and are constrained by the approximate chiral symmetry manifested in QCD. This article provides a clear introduction to chiral symmetry and the Skyrme model, and discusses the Skyrme model's relation to the chiral bag model, its extensions, and its application to nucleons and hyperons.

The three articles of the present volume pertain to very different subjects, all ofconsiderable current interest. The first reviews the fascinating history ofthe search for nucleon substructure in the nucleus using the strength ofGamow- Teller excitations. The second deals with deep inelastic lepton scattering as a probe ofthe non-perturbative structure of the nucleon. The third describes the present state ofaffairs for muon catalyzed fusion, an application of nuclear physics which many new experiments have helped to elucidate. This volume certainly illustrates the broad range ofphysics within our field. The article on Nucleon Charge-Exchange Reactions at Intermediate Energy, by Parker Alford and Brian Spicer, reviews recent data which has clarified one of the greatest puzzles of nuclear physics during the past two decades, namely, the "missing strength" in Gamow-Teller (GT) transitions. The nucleon-nucleon interaction contains a GT component which has a low-lying giant resonance. The integrated GT strength is subject to a GT sum rule. Early experiments with (n, p) charge exchange reactions found only about half of the strength, required by the sum rule, in the vicinity of the giant resonance. At the time, new theoretical ideas suggested that the GT strength was especially sensitive to renormalization from effects pertaining to nucleon substructure, particularly the delta excitation of the nucleon in the nucleus.

This volume of Advances in Nuclear Physics addresses two very different frontiers of contemporary nuclear physics - one highly theoretical and the other solidly phenomenological. The first article by Matthias Burkardt provides a pedagogical overview of the timely topic of light front quantization. Although introduced decades ago by Dirac, light front quantization has been a central focus in theoretical - clear and particle physics in recent years for two majorreasons. The first, as discussed in detail by Burkardt, is that light-cone coordinates are the natural coordinates for describing high-energy scattering. The wealth of data in recent years on nucleon and nucleus structure functions from high-energy lepton and hadron scattering thus provides a strong impetus for understanding QCD on the light cone. Second, as theorists have explored light front quantization, a host of deep and intriguing theoretical questions have arisen associated with the triviality of the vacuum, the role of zero modes, rotational invariance, and renormalization. These issues are so compelling that they are now intensively investigated on their own merit, independent of the particular application to high-energy scattering. This article provides an excellent introduction and overview of the motivation from high-energy scattering, an accessible - scription of the basic ideas, an insightful discussion of the open problems, and a helpful guide to the specialized literature. It is an ideal opportunity for those with a spectator's acquaintance to develop a deeper understanding of this important field.

Nuclear many-body theory provides the foundation for understanding and exploiting the new generation of experimental probes of nuclear structure that are now becoming available. The twentieth volume of Advances in Nuclear Physics is thus devoted to two major theoretical chapters addressing two fundamental issues: understanding single-particle properties in nuclei and the consistent formulation of a relativistic theory appropriate for hadronic physics. The long-standing problem of understanding single-particle behavior in a strongly interacting nuclear system takes on new urgency and sig nificance in the face of detailed measurements of the nuclear spectral function in (e, e'p) experiments. In the first chapter, Mahaux and Sartor confront head-on the ambiguities in defining single-particle properties and the limitations in calculating them microscopically. This thoughtful chapter provides a thorough, pedagogical review of the relevant aspects of many body theory and of previous treatments in the nuclear physics literature. It also presents the author's own vision of how to properly formulate and understand single-particle behavior based on the self-energy, or mass operator. Their approach provides a powerful, unified description of the nuclear mean field that covers negative as well as positive energies and consistently fills in that information that cannot yet be calculated reliably microscopically by a theoretically motivated phenomenology. Particular emphasis is placed upon experiment, both in the exhaustive comparisons with experimental data and in the detailed discussion of the relations of each of the theoretical quantities defined in the chapter to physical observables."

The quest for many-body techniques and approximations to describe the essential physics of strongly interacting systems with many degrees of freedom is one of the central themes of contemporary nuclear physics. The three articles in this volume describe advances in this quest in three dif ferent areas of nuclear many-body physics: multi quark degrees of freedom in nucleon-nucleon interactions and light nuclei, multinucleon clusters in many-nucleon wave functions and reactions, and the nuclear-shell model. In each case the common issues arise of identifying the relevant degrees of freedom, truncating those that are inessential, formulating tractable approximations, and judiciously invoking phenomenology when it is not possible to proceed from first principles. Indeed, the parallels between the different applications are often striking, as in the case of the similarities in the treatment of clusters of quarks in nucleon-nucleon interactions and clusters of nucleons in nuclear reactions, and the central role of the resonating group approximation in treating both. Despite two decades of effort since the experimental discovery of quarks in nucleons, we are still far from a derivation of nucleon structure and nucleon-nucleon interactions directly from quantum chromodynamics."

The four articles of the present volume address very different topics in nuclear physics and, indeed, encompass experiments at very different kinds of exp- imental facilities. The range of interest of the articles extends from the nature of the substructure of the nucleon and the deuteron to the general properties of the nucleus, including its phase transitions and its rich and unexpected quantal properties. The first article by Fillipone and Ji reviews the present experimental and theoretical situation pertaining to our knowledge of the origin of the spin of the nucleon. Until about 20 years ago the half-integral spin of the neutron and p- ton was regarded as their intrinsic property as Dirac particles which were the basic building blocks of atomic nuclei. Then, with the advent of the Standard Model and of quarks as the basic building blocks, the substructure of the - cleon became the subject of intense interest. Initial nonrelativistic quark m- els assigned the origin of nucleon spin to the fundamental half-integral spin of its three constituent quarks, leaving no room for contributions to the spin from the gluons associated with the interacting quarks or from the orbital angular momentum of either gluons or quarks. That naive understanding was shaken, about fifteen years ago, by experiments involving deep-inelastic scattering of electrons or muons from nucleons.

The two comprehensive reviews in this volume address two fundamental problems that have been of long-standing interest and are the focus of current effort in contemporary nuclear physics: exploring experimentally the density distributions of constituents within the nucleus and understand ing nuclear structure and interactions in terms of hadronic degrees of freedom. One of the major goals of experimental probes of atomic nuclei has been to discover the spatial distribution of the constituents within the nucleus. As the energy and specificity of probes have increased over the years, the degree of spatial resolution and ability to select specific charge, current, spin, and isospin densities have correspondingly increased. In the first chapter, Batty, Friedman, Gils, and Rebel provide a thorough review of what has been learned about nuclear density distributions using electrons, muons, nucleons, antinucleons, pions, alpha particles, and kaons as probes. This current understanding, and the limitations thereof, are crucial in framing the questions that motivate the next generation of experimental facilities to study atomic nuclei with electromagnetic and hadronic probes. The second chapter, by Machleidt, reviews our current understanding of nuclear forces and structure in terms of hadronic degrees of freedom, that is, in terms of mesons and nucleons. Such an understanding in terms of hadronic variables is crucial for two reasons. First, since effective hadronic theories are quite successful in describing a broad range of phenomena in low-energy nuclear physics, and there are clear experimental signatures of meson exchange currents in nuclei, we must understand their foundations."