This work summarises the salient features of current and planned experiments into multiquark hadrons, describing various inroads to accommodate them within a theoretical framework. At a pedagogical level, authors review the salient aspects of quantum chromodynamics (QCD), the theory of strong interactions, which has been brought to the fore by high-energy physics experiments over recent decades. Compact diquarks as building blocks of a new spectroscopy are presented and confronted with alternative explanations of the XYZ resonances. Ways to distinguish among theoretical alternatives are illustrated, to be tested with the help of high luminosity LHC, electron-positron colliders, and the proposed Tera-Z colliders. Non-perturbative treatments of multiquark hadrons, such as large N expansion, lattice QCD simulations, and predictions about doubly heavy multiquarks are reviewed in considerable detail. With a broad appeal across high-energy physics, this work is pertinent to researchers focused on experiments, phenomenology or lattice QCD.

A comprehensive summary of current research into multiquark hadrons, describing them in terms of constituent quarks, gluons and compact diquarks.

In August 1979 a group of 94 physicists from 60 laboratories in 21 countries met in Erice to attend the 17th Course of the International School of Subnuclear Physics. The countries represented at the School were: Argentina, Australia, Austria, Belgium, Canada, Federal Republic of Germany, France, Hungary, India, Italy, Japan, Korea, the Netherlands, Nor way, Poland, Rumania, Spain, Sweden, the United Kingdom, the United States of America, and Yugoslavia. The School was sponsored by the Italian Ministry of Public Education (MPI), the Italian Ministry of Scientific and Techno logical Research (MRST) , the Sicilian Regional Government, and the Weizman Institute of Science. In the theoretical sessions, as expected, Sidney Coleman's (liN) lectures provided a new masterpiece in his Erice series. Andre Martin lectured on the theory of new particles, R.L. Jaffe on the Bag Hodel and Francis E. Low on quark status at low energy. In the more specialized section we were able to reflect on the problem of asymptotic changes in gauge theory, troubles experienced with instantons and finally on the fate of false vacua, thanks to A. Patrascioiu, R. Petronzio, and H. Kleinert. A quite exceptional event this year was the special QCD session wId_ch I leave the reader to enjoy without further introduction.

Novel forms of matter, such as states made of gluons (glueballs), multiquark mesons or baryons and hybrid mesons are predicted by low energy QCD, for which several candidates have recently been identified. Searching for such exotic states of matter and studying their production and decay properties in detail has become a flourishing field at the experimental facilities now available or being built - e.g. BESIII in Beijing, BELLE II at SuperKEKB, GlueX at Jefferson Lab, PANDA at FAIR, J-PARC and in the upgraded LHC experiments, in particular LHCb. A modern primer in the field is required so as to both revive and update the teaching of a new generation of researchers in the field of QCD. These lectures on hadron spectroscopy are intended for Master and PhD students and have been originally developed for a course delivered at the Stefan Meyer Institute of the Austrian Academy of Sciences. They are phenomenologically oriented and intended as complementary material for basic courses in particle and nuclear physics. The book describes the spectra of light and heavy mesons and baryons, and introduces the fundamental properties based on symmetries. Further, it derives multiplet structures, mixing angle, decay coupling constants, magnetic moments of baryons, and predictions for multiquark states and compares these with suitable experimental data. Basic methods of calculating decay angular distributions and determining masses and widths of resonances are also presented. The appendices provide students and newcomers to the field with the necessary background information, and include a set of problems and solutions.

This third book on Quark-Gluon plasma and heavy ion collisions follows the previous ones, published in 1988 and 2005, that described theoretical proposals for a large program, and then the QGP discovery at RHIC.The present one describes the rather mature field, with extensive program at RHIC and LHC colliders and corresponding theory. QGP turns out to be a strongly coupled medium made up of quarks and gluons, existing in exploding fireballs. It is the hottest form of matter created in a laboratory. Other subjects discussed in the book are QCD vacuum structure, including topological solitons and nonperturbative phenomena. It also includes some recent progress in theory of hadrons, bridging hadronic spectroscopy with partonic observables.

Proceedings of a NATO ASI held in Cargese, France, August 8-18, 1989