An Axiomatic Approach to Semiclassical Perturbative Gauge Field Theories

Different approaches to axionatic field theory are investigated. The main notions of semiclassical theory are the following: semiclassical states, Poincare transformations, semiclassical action form, semiclassical gauge equivalence and semiclassical field. If the manifestly covariant approach is used, the notion of semiclassical state is related to Schwinger sourse, while the semicalssical action is presented via the R-function of Lehmann, Symanzik and Zimmermann. Semiclassical perturbation theory is constructed. Its relation with the S-matrix theory is investigated. Semiclassical electrodynamics and non-Abelian gauge theories are studied, making us of the Gupta-Bleuler and BRST approaches.Comment: 54 page

An Axiomatic Approach to Semiclassical Field Perturbation Theory

Semiclassical perturbation theory is investigated within the framework of axiomatic field theory. Axioms of perturbation semiclassical theory are formulated. Their correspondence with LSZ approach and Schwinger source theory is studied. Semiclassical S-matrix, as well as examples of decay processes, are considered in this framework.Comment: 32 pages, LaTeX, margins are corrected due to problems with viewing the PostScript fil

Large-N Theory from the Axiomatic Point of View

The state space and observables for the leading order of the large-N theory are constructed. The obtained model ("theory of infinite number of fields") is shown to obey Wightman-type axioms (including invariance under boost transformations) and to be nontrivial (there are scattering processes, bound states, unstable particles etc). The considered class of exactly solvable relativistic quantum models involves good examples of theories containing such difficulties as volume divergences associated with the Haag theorem, Stueckelberg divergences and infinite renormalization of the wave function.Comment: 46 pages, LaTe

Exactly Solvable Quantum Mechanical Models with Infinite Renormalization of the Wave Function

The main difficulty of quantum field theory is the problem of divergences and renormalization. However, realistic models of quantum field theory are renormalized within the perturbative framework only. It is important to investigate renormalization beyond perturbation theory. However, known models of constructive field theory do not contain such difficulties as infinite renormalization of the wave function. In this paper an exactly solvable quantum mechanical model with such a difficulty is constructed. This model is a simplified analog of the large-N approximation to the $\Phi\phi^a\phi^a$-model in 6-dimensional space-time. It is necessary to introduce an indefinite inner product to renormalize the theory. The mathematical results of the theory of Pontriagin spaces are essentially used. It is remarkable that not only the field but also the canonically conjugated momentum become well-defined operators after adding counterterms.Comment: 13 pages, LaTe

States and Observables in Semiclassical Field Theory: a Manifestly Covariant Approach

A manifestly covariant formulation of quantum field Maslov complex-WKB theory (semiclassical field theory) is investigated for the case of scalar field. The main object of the theory is "semiclassical bundle". Its base is the set of all classical states, fibers are Hilbert spaces of quantum states in the external field. Semiclassical Maslov states may be viewed as points or surfaces on the semiclassical bundle. Semiclassical analogs of QFT axioms are formulated. A relationship between covariant semiclassical field theory and Hamiltonian formulation is discussed. The constructions of axiomatic field theory (Schwinger sources, Bogoliubov $S$-matrix, Lehmann-Symanzik-Zimmermann $R$-functions) are used in constructing the covariant semiclassical theory. A new covariant formulation of classical field theory and semiclassical quantization proposal are discussed.Comment: 20 pages, LaTeX, margins are corrected due to problems with viewing PostScript fil

HIGH ORDER BEHAVIOUR OF PERTURBATION RECURSIVE RELATIONS

The problem of large order behaviour of perturbation theory for quantum mechanical systems is considered. A new approach to it is developed. An explicit mechanism showing the connection between large order recursive relations and classical euclidean equations of motion is found. Large order asymptotics of the solution to the recursive relations is constructed. The developed method is applicable to the excited states, as well as to the ground state. Singular points of the obtained asymptotics of the perturbation series for eigenfunctions and density matrices are investigated and formulas being valid near such points are obtained.Comment: 30 pages, LaTeX, 6 figures can be obtained from the autho

LARGE ORDER ASYMPTOTICS OF SEMICLASSICAL EXPANSION: A NEW APPROACH

A new approach to the problem of finding the asymptotical behaviour of large orders of semiclassical expansion is suggested. Asymptotics of high orders not only for eigenvalues, but also for eigenfunctions, are constructed. Thus, one can apply not only functional integral technique, which has been used up to now, but also method of direct analysis of the semiclassical expansion recursive relations.Comment: 24 pages, LaTeX, 4 figures can be obtained from the author, revised russian version is submitted to Yadernaya Fizik

Instability of Space-Time due to Euclidean Wormholes

The problem of topology change transitions in quantum gravity is discussed. We argue that the contribution of the Giddings-Strominger wormhole to the Euclidean path integral is pure imaginary. This is checked by two techniques: by the functional integral approach and by the analysis of the Wheeler-De Witt equation. We present also a simple quantum mechanical model which shares many features of the system consisting of parent and baby universes. In this simple model, we show that quantum coherence is completely lost and obtain the equation for the effective density matrix of the ''parent universe''.Comment: 9 pages in LaTeX, 3 figures in PostScript, to appear in Proceedings of the 9th International Seminar "QUARKS-96

Renormalization of the Semiclassical Hamiltonian Field Theory

The Hamiltonian approach to the quantum field theory is considered. Since there are additional difficulties such as the Haag theorem and Stueckelberg divergences, renormalization of the time-dependent dynamical quantum field theory is much more complicated than renormalization of the S-matrix. It is necessary to consider the regularized theory with ultraviolet and infrared cutoffs and impose the conditions not only on the dependence of the Hamiltonian on the cutoffs (as usual) but also on the dependence of the initial states. It happens that one should consider the initial states to be singulary dependent on the cutoffs in order to avoid the Stueckelberg divergences. Different types of semiclassical approximations to quantum theory are discussed. It happens that the method of quantizing classical solutions to field equations corresponds not to the WKB-approach but to the complex-WKB theory. The problem of imposing conditions on the semiclassical initial states is discussed. Different prescriptions for choice of initial conditions are analysed.Comment: Talk presented at the International Seminar "Quarks-98", Suzdal, Russia, May 17-24, 1998, 12 pages in LaTeX, 1 postscript figur

A Negative Mode About Euclidean Wormhole

Wormholes -- solutions to the euclidean Einstein equations with non-trivial topology -- are usually assumed to make real contributions to amplitudes in quantum gravity. However, we find a negative mode among fluctuations about the Giddings-Strominger wormhole solution. Hence, the wormhole contribution to the euclidean functional integral is argued to be purely imaginary rather than real, which suggests the interpretation of the wormhole as describing the instability of a large universe against the emission of baby universes.Comment: 9 pages in LaTeX, 1 figure in PostScrip