[en] Recent work on Euler hierarchies of field theory Lagrangians iteratively constructed from their successive equations of motion is briefly reviewed. On the one hand, a certain triality structure is described, relating arbitrary field theories, classical topological field theories - whose classical solutions span topological classes of manifolds - and re-parametrisation invariant theories - generalizing ordinary string and membrane theories. On the other hand, finite Euler hierarchies are constructed for all three classes of theories. These hierarchies terminate with universal equations of motion, probably defining new integrable systems as they admit an infinity of Lagrangians. Speculations as to the possible relevance of these theories to quantum gravity are also suggested. (author) 13 refs

[en] These notes are in two parts. The first consists of a colloquium. Its aim was to give a general introduction and review of these theories, which could provide a unified theory of all interactions. The second consists of lectures. They give a description of the structure and spectra of the bosonic, spinning, supersymmetric and heterotic string theories

[en] The coupling to abelian background gauge fields of closed bosonic strings compactified on a torus is considered. There exist specific field configurations for which the theory cannot be defined consistently, in spite of the fact that the field equations of motion are then solved exactly. This critical behaviour is related to a breakdown of local and global world-sheet symmetries, as well as of spacetime unitarity. A physical interpretation of this phemomenon is proposed. The issue of spacetime duality is also discussed. This symmetry is shown to be partially broken for generic background field configurations. (orig.)

[en] Abstract only

[en] Recent and on-going experimental programs pursued by the Louvain-la-Neuve/ETH-Zurich/Madison group for precision measurements of positron longitudinal polarisation in nuclear β-decay of ¹⁰⁷In and ¹²N are discussed. Results obtained so far in first generation measurements are reviewed; new developments towards second generation measurements are described. All these experiments are sensitive to deviations from the maximally parity violating assumption implicit in the Standard Model. In particular, they lead to competitive lower bounds on the mass of hypothetical charged gauge bosons coupling to the right-handed fermions. Other case studies for such tests are also mentioned

[en] Using the Batalin-Fradkin-Vilkovisky formalism for constrained systems, the space-phase path-integral representation of the free bosonic string propagator is considered and compared with the Polyakov approach. A Gribov problem exists for this system with the consequence that the integration measure over modular space is left undetermined. The authors initially consider the case of the scalar particle with special emphasis on analogies with the string case. The question of Wick rotations in modular space is also discussed

[en] We discuss how Virasoro anomalies in open string theories uniquely select the gauge group SO(2^D/2) independently of any regularisation, although the cancellation of these anomalies does not occur in tachyonic theories, and regulators can always be chosen to make these theories (one-loop) finite for any SO(n) and USp(n) gauge group. The discussion is mainly restricted to open bosonic strings. These results open new perspectives for the recent suggestion made by Sagnotti, the generalisations of which allow for the construction of new open string theories in less than ten dimensions. (orig.)

[en] Causal rigid particles whose action includes an arbitrary dependence on the world-line extrinsic curvature are considered. General classes of solutions are constructed, including causal tachyonic ones. The Hamiltonian formulation is developed in detail except for one degenerate situation for which only partial results are given and requiring a separate analysis. However, for otherwise generic rigid particles, the precise specification of Hamiltonian gauge symmetries is obained with in particular the identification of the Teichmueller and modular spaces for these systems. Finally, canonical quantisation of the generic case is performed paying special attention to the phase space restriction due to causal propagation. A mixed Lorenz-gravitational anomaly is found in the commutator of Lorentz boosts with world-line reparametrisations. The subspace of gauge invariant physical states is therefore not invariant under Lorentz transformations. Consequences for rigid strings and membranes are also discussed. (orig.)

[en] Using the Batalin-Fradkin-Vilkovisky formalism for constrained systems, BRST quantisation of bosonic and spinning string theories is introduced. As a warm-up exercise, the case of the scalar point-particle is first considered. (orig.)

[en] Anomaly and decoupling constraints are used in an extensive search for acceptable five preon composite models. We show that the hypercolor group cannot be simple, except for two cases, and that it is difficult to find asymptotically free solutions. We give a general class of solutions for n-preon composites based on SU(n) x SU(n). (orig.)