This volume reviews recent developments in conformal quantum field theory in D-dimensions, and focuses on two main aims. Firstly, the promising trend is followed toward constructing an exact solution for a certain class of models. Work on the conformal Ward identities in a D-dimensional space in the late '70s suggests a parallel with the null-vectors which determine the minimal models in the two-dimensional field theory. Recent research has also indicated the possible existence of an infinite parameter algebra analogous to the Virasoro algebra in spaces of higher dimensions D>=3. Each of these models contains parameters similar to the central charge of the two-dimensional theory, due to special fields which occur in the commutator of the components of the energy-momentum tensor. As a first step, a special formalism is suggested which allows finding an exact solution of these models for any space dimension. Then it is shown that in each model closed differential equations can be obtained for higher correlators, as well as the algebraic equations for scale dimensions of fields, and dimensionless parameters similar to the central charge. Secondly, this work aims to give a survey of some special aspects of conformal quantum field theory in D-dimensional space. Included are the survey of conformal methods of approximate calculation of critical indices in a three-dimensional space, an analysis and solution of a renormalised system of Schwinger-Dyson equations, a derivation of partial wave expansions, among other topics. Special attention is given to the development of the apparatus of quantum conform theory of gauge fields. Audience: This book will be of interest to graduate students andresearchers whose work involves quantum field theory.

This book contains a systematic analysis of the formalisms of quantum electro dynamics in the presence of an intense external field able to create pairs from the vacuum, and thereby violate the stability of the latter. The approach developed is not specific to quantum electrodynamics, and can equally well be applied to any quantum field theory with an unstable vacuum. It should be noted that only macroscopic external fields are considered, whereas problems associated with the superstrong Coulomb (micro) field are not treated. As a rule, the discussion is confined to those details of the formalism and calculations that are specific to the instability property. For instance, renormalization is not discussed here since, in practical calculations, it is carried out according to standard methods. The presentation is based mainly on original research undertaken by the authors. Chapter 1 contains a general introduction to the problem. It also presents some standard information on quantum electrodynamics, which will be used later in the text. In addition, an interpretation of the concept of an external field is given, and the problems that arise when one tries to keep the interaction with the external field exactly are discussed. In Chapter 2, the perturbation expansion in powers of the radiative interac tion is developed for the matrix elements of transition processes, taking the arbitrary external field into account exactly."

Our prime concern in this book is to discuss some most interesting prosppcts that have occurred recently in conformally invariant quantum field theory in a D-diuwnsional space. One of the most promising trends is constructing an pxact solution for a cprtain class of models. This task seems to be quite feasible in the light of recent resllits. The situation here is to some extent similar to what was going on in the past ypars with the two-dimensional quantum field theory. Our investigation of conformal Ward identities in a D-dimensional space, carried out as far hack as the late H. J7Gs, showed that in the D-dimensional quantum field theory, irrespective of the type of interartion, there exists a special set of states of the field with the following property: if we rpqllire that one of these states should vanish, this determines an exact solution of 3. certain field model. These states are analogous to null-vectors which determine the minimal models in the two-dimensional field theory. On the other hand, the recent resparches supplied us with a number of indications on the existencp of an intinite-parampter algebra analogous to the Virasoro algebra in spaces of higher dimensions D 2: :~. It has also been shown that this algebra admits an operator rentral expansion. It seems to us that the above-mentioned models are field theoretical realizations of the representations of these new symmetries for D 2: ;3.