[en] We study the width of the confining string between static quarks in Abelian lattice gauge theories using strong coupling expansions. We consider gauge groups Zsub(n) and U(1) in 3 and 4 dimensions. This extends previous work with Luescher, where SU(2) and Z₂ were studied. In ν = 3 dimensions we find evidence for a roughening transition. It is characterized by a divergence of the string width for an infinitely far separated quark antiquark pair, while the string tension remains non-zero. In ν = 4 dimensions for the Abelian groups we do not have evidence for a roughening transition away from a phase transition. (orig.)

[en] An introduction to recent works, in S-matrix theory and axiomatic field theory, on the analysis and derivation of momentum-space analyticity properties of the multiparticle S matrix is presented. It includes an historical survey, which outlines the successes but also the basic difficulties encountered in the sixties in both theories, and the evolution of the subject in the seventies

No abstract available

[en] Noclear reactions: Four-body problem. Effective two-body equations with exact (2+2)-subsystem contributions. Relation to field-theoretical model by Fonseca and Shanley. Three-body propagator with exchange effects. (orig.)

[en] An approximate QCD vacuum for SU(N→infinity) is presented. It is a generalization of the ferromagnetic vacuum first obtained by Savvidy for SU(2) and generalized to SU(3) and SU(4). Problems occurring for N>=5 are handled in the large N limit by a continuous formalism, and the vacuum obtained is characterized by N-1 constant, commuting, colormagnetic fields with an isotropic distribution of spatial directions. The energy density of this vacuum is lower than that of the perturbative vacuum by a number proportional to N², as expected from general large N arguments. Like the Savvidy vacuum the large N vacuum may decay into a variant of the domained Copenhagen vacuum. A lower limit on the domain size is given. (Auth.)

[en] Unexpected phase structure in four dimensional lattice gauge theory based on the groups SO(3) and SU(5) have prompted studies of variations on the Wilson action for SU(2). A rich phase structure related to the decomposition of SU(2) into SO(3) and Z₂ is found. The scale of asymptotic freedom has a dramatic dependence on the choice of lattice action

[en] It is shown that the exchange contribution to the electron-proton potential Born term in elastic electron-hydrogen atom scattering arises as the non relativistic limit from the exchange of a proton between the two participant electrons - calculated from quantum electrodynamics including properly bound states (as solution of Bethe - Salpeter equation). (Author)

[en] The authors determine the transition points βsub(c) and plaquette energies Esub(p) of U(1), SU(2) and SO(3) lattice gauge theories in 4 and 5 dimensions by mean-field methods, and compare with corresponding values determined by the Monte-Carlo technique. In every case, the mean-field and Monte-Carlo values for βsub(c) and Esub(p) agree to within a few percent. (Auth.)

[en] The general properties of the factorized S matrix in two-dimensional space-time are considered. The relation between the factorization property of the scattering theory and the infinite number of conservation laws of the underlying field theory is discussed. The factorization of the total S matrix is shown to impose hard restrictions on two-particle matrix elements: they should satisfy special identities, the so-called factorization equations. The general solution of the unitary, crossing and factorization equations is found for the S matrices having isotopic O(N) symmetry. The solution turns out to have different properties for the cases N=2 and N >= 3. The solution for N=2 is shown to be an exact soliton S matrix of the sine-Gordon model (equivalently the massive Thirring model). The total S matrix of the model is constructed. In the case of N >= 3 there are two ''minimum'' solutions, i.e., those having a minimum set of singularities. One of them is shown to be an exact S matrix of the quantum O(N)-symmetric nonlinear sigma - model, the other is argued to describe the scattering of elementary particles of the Gross-Neveu model

[en] The study is devoted to the problems of a nonlinear development of gas dynamical instability in the framework of a two-dimensional boundary problem with initial data. The classical equations of gas dynamics and monoliquid magnetic hydrodynamics (MHD) are used. Taking into account application to cosmic objects general relativistic equations of gas dynamics and electromagnetic two-liquid gas dynamics for electrons and ions are investigated. The model of the super nova flare, based on the development of the two-dimensional axially symmetric convective instability inside it is considered. Criteria derivation of MHD stability of equilibrium configurations of the arbitrary toroidal geometry stability is presented