Spontaneous chiral symmetry breaking, mesons and baryons are illustrated in the language of the Dirac theory. Various forces acting between quarks inside baryons are discussed. I explain why the naive quark models typically overestimate pentaquark masses by some 500 MeV and why in the fully relativistic approach to baryons pentaquarks turn out to be light. I discuss briefly why it can be easier to produce pentaquarks at low than at high energies.

The assumption of strong diquark correlations in the QCD spectrum suggests flavor multiplets of hadrons that are degenerate in the chiral limit. Generally it would be unnatural for there to be degeneracy in the hadron spectrum that is not protected by a QCD symmetry. Here we show--for pentaquarks constructed from diquarks--that these degeneracies can be naturally protected by the full chiral symmetry of QCD. The resulting chiral multiplet structure recovers the ideally-mixed pentaquark mass spectrum of the diquark model, and interestingly, requires that the axial couplings of the pentaquarks to states outside the degenerate multiplets vanish in the chiral limit. This result suggests that if these hadrons exist, they are stable in the chiral limit and therefore have widths that scale as the fourth power of the kaon mass over the chiral symmetry breaking scale. Natural-size widths are of order a few MeV.

We review lattice calculations of pentaquarks and discuss issues pertaining to interpolation fields, distinguishing the signal of pentaquarks from those of the KN scattering states, chiral symmetry, and ghost state contaminations.

This proceedings volume collected papers presented at a recent symposium on Chiral Symmetry in Hadrons and Nuclei — the seventh in a series of international symposia — with an aim of providing a platform for discussions among the experts and an overview of the present status in the hadron and nuclear physics related to the chiral symmetry.The recent past years have seen a remarkable progress towards a unified description of nonperturbative strong interaction phenomena based on the fundamental theory of the strong interaction, Quantum ChromoDynamics, and Effective Field Theories. The topics discussed in these proceedings include: chiral and heavy-quark spin symmetry; chiral dynamics of few-body hadron systems; chiral symmetry and hadrons in a nuclear medium; chiral dynamics in nucleon-nucleon interaction and atomic nuclei; chiral symmetry in rotating nuclei; hadron structure and interactions; exotic hadrons, heavy flavor hadrons and nuclei; mesonic atoms and nuclei.

Chiral symmetry, a basic symmetry of the strong interaction and thus of QCD, plays a major role in low energy hadron physics. This workshop highlighted its importance for the understanding of hadron properties, hadron matter and recent precise lattice and experimental results. Besides, heavy quark physics was also addressed.

The theoretical understanding of elementary particle interactions has under gone a revolutionary change during the past one and a half decades. The spontaneously broken gauge theories, which in the 1970s emerged as a prime candidate for the description of electro-weak (as weIl as strong) interactions, have been confirmed by the discovery of neutral weak currents as weIl as the w- and Z-bosons. We now have a field theory of electro-weak interactions at energy scales below 100 GeV-the Glashow-Weinberg-Salam theory. It is a renormalizable theory which enables us to do calculations without en countering unnecessary divergences. The burning question now is: Wh at lies ahead at the next level of unification? As we head into the era of supercolliders and ultrahigh energy machines to answer this question, many ap, pealing possi bilities exist: left-right symmetry, technicolor, compositeness, grand unifica ti on, supersymmetry, supergravity, Kaluza-Klein models, and most recently superstrings that even unify gravity along with other interactions. Experi ments will decide if any one or any combination of these is to be relevant in the description of physics at the higher energies. As an outcome of our con fidence in the possible scenerios for elementary particle physics, we have seen our understanding of the early uni verse improve significantly.

The papers collected in this book represent an exciting contribution to the growing body of experimental and theoretical research into exotic hadrons. The prime focus of the volume is the latest work on pentaquark baryons.The in-depth experimental reports cover both positive and negative evidence for the existence of various combinations of particles, and photo-electro production, hadronic production and high-energy processes are discussed in detail.Important theoretical areas of current interest are considered, including chiral solitons, constituent quarks, the QCD sum rule, lattice QCD, production reactions, and the determination of spin and parity. The volume features the work of two pioneering theorists, H Lipkin and D Diakonov, among the comprehensive coverage of the latest theoretical ideas in the field.The proceedings have been selected for coverage in:• Index to Scientific & Technical Proceedings® (ISTP® / ISI Proceedings)• Index to Scientific & Technical Proceedings (ISTP CDROM version / ISI Proceedings)• CC Proceedings — Engineering & Physical Sciences