[en] The paper proposes a model of a unitary quantum field theory where the particle is represented as a wave packet. The frequency dispersion equation is chosen so that the packet periodically appears and disapears without changing its form. The envelope of the process is identified with a conventional wave function. Equations of such a field are nonlinear and relativistically invariant. With proper adjustements they reduce to Dirac, Schroedinger and Hamilton-Jacobi equations. A number of new experimental effects are predicted both for high and low energies

[en] We investigate the relation between finiteness of a four-dimensional quantum field theory and global supersymmetry. To this end we consider the most general quantum field theory and analyse the finiteness conditions resulting from the requirement of the absence of divergent contributions to the renormalizations of the parameters of the theory. In addition to the gauge bosons, both fermions and scalar bosons turn out to be a necessary ingredient in a non-trivial finite gauge theory. In all cases discussed, the supersymmetric theory restricted by two well-known constraints on the dimensionless couplings proves to be the unique solution of the finiteness conditions. (Author)

[en] It is pointed out that both classical Wheeler-Feynman electrodynamics and its finite quantized generalization inevitably lead to microscopic causality violation. As there is some evidence for such effects in proton Compton scattering, there is possibly reason to prefer such absorber theories of action at a distance over field theories as the more reasonable microscopic description of nature

[en] The book contains the 11 lectures given at the Trieste Conference on Topological Methods in Quantum Field Theories held between 11-15 June 1990. A separate abstract has been prepared for each lecture. Refs and figs

[en] In a trial exploration of the discrete spectra of observables in a quantum theory of gravitation the author has previously suggested the construction of superclasses and the evaluation within them of closed-path phase integrals. Superclasses are sets of ordinary equivalence classes where the homology group is non-trivial. In this paper it is suggested that even the equivalence classes themselves, in general relativity, have a homology rich enough so that at least a few phase integrals can be formed without the need to construct superclasses. As a plausible example let us take space times asymptotically flat at spatial infinity. It would appear that the total angular moment (if this integral is finite) can be quantified by the phase integral method. It is not known at present whether other discrete-spectrum observables can be studied by this method

[en] Theoretical physicists, coming from different countries, working on different areas, gathered at Positano: the Proceedings contain all the lectures delivered as well as contributed papers. Many areas of physics are represented, elementary particles in high energy physics, quantum relativity, quantum geometry, condensed matter physics, statistical mechanics; but all works are concerned with the use of the methods of quantum field theory. The first motivation of the meeting was to pay homage to a great physicist and a great friend; it was also an occasion in which theoretical physicists got together to discuss and to compare results in different fields. The meeting was very intimate; the relaxed atmosphere allowed constructive discussions and contributed to a positive exchange of ideas. (orig.)

[en] It is shown that very intensive gravitational fields (as those in the black-hole proximity) give rise the other interactions of the nature, taking advantage of the gravitational energy and due to the manifestation of suitable symmetries.(Author)

[en] Einstein's gravitational field equation is deduced from the hypothesis of background field action of stochastic nature. (Author)

[en] We study the consequences of finiteness for a general renormalizable quantum field theory by analysing the finiteness conditions resulting from the requirement of absence of divergent contributions to the renormalizations of the parameters of an arbitrary gauge theory. In all cases considered, the well-known two-loop finite supersymmetric theories prove to be the unique solution of the finiteness criterion. (Author)

[en] The author discusses the general principles underlying quantum field theory and attempts to identify its most profound consequences. The deepest of these consequences result from the infinite number of degrees of freedom invoked to implement locality. A few of quantum field theory close-quote s most striking successes, both achieved and prospective are mentioned, and possible limitations of the theory are viewed in the light of its history. copyright 1999 The American Physical Society