[en] Based on quantum chromodynamics and on the modern theory of strong interaction the thermodynamical properties of quark-gluon plasma are investigated. Quantization methods of classical gauge theories without gauge fixing are briefly reviewed. The definition of finite temperature Green-functions and the application to the asymptotically free quark-gluon gas are given. The lattice gauge theory and its classical vacuum configurations are investigated. A method of Monte Carlo calculation for the finite temperature SU(2) lattice gauge theory was developed. Numerical results are presented. The question of phase transition between nucleon and quark-gluon phase is discussed. (D.Gy.)

[en] By enlarging the functional space to include nonlocal fields which are sensitive to the space-time asymptotics of the configurations the Θ-sectors in the OS-Hilbert space were formally constructed. The question of inequivalence of the different Θ-sectors was studied on two quantum mechanical examples and in the case of non-Abelian gauge theories. (author)

[en] Non-local order parameters are constructed to test confinement, deconfinement and broken charge symmetry phases of lattice gauge theories with matter fields. The relation of these classical fields to the structure of the quantum theory is analyzed. In the case of the Z(2) Higgs model the author explicitely constructs a charged sector in the free-charge phase. The confinement-screening phase turns out to be split into two phases from the stand-point of non-local fields. This phase transition can be interpreted as the breaking of the global gauge symmetry. (author)

[en] The authors propose a physical picture and a non-perturbative definition of confinement in lattice gauge theories with matter fields. They argue that in the thermodynamical limit the fractional (baryon) charges become unobservable in the confinement phase for all local measurements. As an illustration they have tested the criterion in three of the possible phases of the Z(N) matter-gauge system by means of perturbation theory. They have found that the usual confinement and Higgs phases show confinement, while the free phase contains fractionally charged states contributing to local physical quantitites. (author)

[en] The concept of the loop group describes a conformal model in terms of bounded operators. The simplest possibility, the central extended U(1) loop group algebra spanned by operators W(f), f:S¹→R satisfying Weyl algebra relations is considered. The possibility that the loop group element e^if represented by W(f) does not necessarily lie in the identity component is investigated. This leads to a quantization of the level parameter k in the cocycle. Considering this 'large' loop group algebra as the algebra of observables, their Z_k type of superselection sectors is studied, and fields are constructed that create the Z_k charges. The commutation relations of these fields turn out to be of the parafermion type. (K.A.) 4 refs

[en] Numerical evidence for the phase transition between the confinement phase and free Coulomb phase of SU(2) Yang-Mills theory with lattice cut-off is given. The search for the critical temperature is based on a Monte Carlo study of the string tension between a heavy Q anti Q-pair in heat bath. The arbitrary normalization 0.2 GeV² is used for the string tension at zero temperature when a smooth extrapolation of the lattice theory to the continuum limit is carried out. The numerical estimate for the critical temperature Tsub(c) approximately 160 +- 30 MeV in the absence of quark degrees of freedom is given. It is suggestive that the phase transition is of second-order. (author)

[en] Three classes of non-local changed fields are identified and speculatively called the theories in the confinement, Higgs and free charge phases, to illustrate by example that these classes are not empty. Preliminary results show that a certain generalization of the Coulomb field to compact gauge groups yields a field which creates a state freely propagating in the free charge phase of the 3-dimensional z(2) gauge matter system. (U.K.)

[en] Non-local order parameters are proposed to test the confinement-deconfinement transition in lattice gauge-matter systems. We construct a charged sector in the free charge phase of the Z(2) Higgs model. We explain why a non-zero expectation value of the Higgs field is possible in the screening region without any physical consequences. (orig.)

[en] In a discretized version of the Georgi-Glashow model, with the tetrahedron group as the gauge group, vector bosons with Z(3) electric charge are constructed in the 'broken' phase. (orig.)

[en] In the two-dimensional spin model with spins taking values in the symmetric group S₃ a solution of the star-triangle equation is found associated to a genus-zero rapidity curve. The solution intersects the physical region of couplings at the point (β*₂, β*₃) = (1/8 ln 2 + 1/6 ln (1+3/√2), 1/3 ln (1+3/√2)). This point is conjectured to be a tricritical point where a non-abelian orbifold symmetry is realized, namely the symmetry described by the Hopf algebra D (S₃), the double of S₃. (orig.)