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[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

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[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