Table of contents

The review summarizes the development of Skyrme's soliton approach to the description of baryon structure. In contrast to existing literature on this subject, the principal attention is devoted not to the pragmatic aspects of the model, but rather to its initial ideas, to its deep topological content and to such subtle problems as the existence of solutions, the attainability of the absolute energy minimum based on the hedgehog ansatz, and so on. It is exactly these features of the Skyrme approach that are, in the authors' opinion, the main advantages compared to other schemes used in strong-interaction physics. The material assembled in the review will, first, enable the reader to gain a deeper understanding of the structure and special features of the Skyrme model and, second, will serve as an adequate base for further modifications and for development of more realistic scenarios of processes in low-energy QCD, the need for which is beyond any doubt.

We describe the anomalies in the electronic properties of zero-gap semiconductors doped with transition elements (iron, chromium) that form deep resonance donor states, i.e., states degenerate with the continuum of the conduction band. We present an analysis of the numerous studies that shows that the distinctiveness of the properties of the materials being discussed, in particular, such a marked anomaly as increased electron mobility with increasing concentration of the dopant, is due to the correlated distribution of the charged donors in the crystal. The study of resonance states in semiconductors is a new field in solid-state physics, which at the same time is of practical interest, since it enables one, for example, to obtain materials with maximal electron mobilities.

A review is given of theoretical and experimental papers on the interaction of acoustic waves with spin waves in ferridielectrics. The region of the resonance interaction—the magnetoacoustic resonance (MAR), in which the interaction is synchronous and is most effective, is discussed in greatest detail. Considerable attention is devoted to nonlinear magnetoacoustic resonance—i.e. to detection of MAR not by absorption, but by generation of higher harmonics of the acoustic wave. The review also discusses the possibilities of using MAR for studying the magnetic and defect structures of crystalline ferridielectrics. The review encompasses practically all the basic papers in this field. The experimental results are systematized, and their correspondence with theory is analyzed.

An analysis is made of the shape of the phase diagrams of substances in the neighborhood of the Lifshitz point, which separates the second-order phase transitions going from the initial phase to a commensurate and to an incommensurate phase. The conclusions of the thermodynamic theory in the mean field approximation and in a treatment including the effects of the interaction of well-developed fluctuations are compared. The possible complication of the phase diagram by a crossing of the line of Lifshitz points with a line of tricritical points and the possible existence of a tricritical Lifshitz point are discussed. The changes in the character of the critical behavior in the neighborhood of the Lifshitz point are discussed in reference to the results of experimental studies of the transformation of anomalies of the thermodynamic characteristics, principally for the proper uniaxial ferroelectrics Sn₂P₂(Se_xS_1–x)₆.

The classical concept of radiation in gauge theories is analyzed. It is concluded from a discussion of three definitions of electromagnetic radiation, i.e., traditional, Dirac's and Teitelboim's definitions, that only the last of these three represents correctly the structure of electromagnetic self-action. Teitelboim's definition is also satisfactory in the non-Abelian case in which the radiation problem is intertwined with that of confinement. The exact solution of the Yang–Mills equations with current formed by an arbitrarily moving color charge is used as a basis for a description of the non-Abelian classical picture. In the confinement phase, the energy of the gauge field is absorbed by the color charge, whereas the deconfinement phase involves the usual emission of radiation, and the color charge (free or accelerated by non-Yang–Mills forces) produces only colorless converging or diverging waves. Certain other fundamental questions concerning classical self-action in Abelian and non-Abelian gauge theories are also examined.