Singularities In Scalar-Tensor Cosmologies

In this article, we examine the possibility that there exist special scalar-tensor theories of gravity with completely nonsingular FRW solutions. Our investigation in fact shows that while most probes living in such a Universe never see the singularity, gravity waves always do. This is because they couple to both the metric and the scalar field, in a way which effectively forces them to move along null geodesics of the Einstein conformal frame. Since the metric of the Einstein conformal frame is always singular for configurations where matter satisfies the energy conditions, the gravity wave world lines are past inextendable beyond the Einstein frame singularity, and hence the geometry is still incomplete, and thus singular. We conclude that the singularity cannot be entirely removed, but only be made invisible to most, but not all, probes in the theory.Comment: 23 pages, latex, no figure

Dynamische Massenerzeugung fuer Quarks und Leptonen

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Proceedings of the 28. international symposium Ahrenshoop on the theory of elementary particles

The following topics were dealt with: elementary particle theory, string theory, algebra, group theory, symmetries, Lie groups, unified field theories, topology and theories of gravitation.ok place from August 30 to September 3, 1994 at Wendisch-Rietz near Berlin. The Symposium was organized jointly by the Institute for Elementary Particle Physics of the Humboldt University of Berlin, the Institute for Theoretical Physics of the University Hannover, the Section of Physics of the University Munich, and DESY Institute for High Energy Physics Zeuthen. It was made possible thanks to the financial support of the Bundesland Brandenburg, the DESY Institute for High Energy Physics Zeuthen, the Walter and Eva Andrejewski Stiftung, and last but not least the Deutsche Forschungsgemeinschaft (DFG). We also would like to thank Karin Pipke for her dedicated assistance to prepare this manuscript. (orig.)Available from TIB Hannover: RA 2999(95-027) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

On the relation of four-dimensional N=2,4 - supersymmetric string backgrounds to integrable models

In this letter we discuss the relation of four-dimensional, N = 2 supersymmetric string backgrounds to integrable models. In particular we show that non-Kaehlerian gravitational backgrounds with one U(1) isometry plus non-trivial antisymmetric tensor and dilaton fields arise as the solutions of the Liouville equation or, for the case of vanishing central charge deficit, as the solutions of the continual Toda equation. When performing an Abelian duality transformation, a particular class of solutions of the continual Toda equation leads to the well-known gravitational Eguchi-Hanson instanton background with self-dual curvature tensor. (orig.)Available from TIB Hannover: RA 2999(94-225) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Moduli dependent non-holomorphic contributions of massive states to gravitational couplings and C"2-terms in Z_N-orbifold compactifications

It is pointed out that massive states in D=4, N=1 supergravity-matter theories can, in general, at the 1-loop level contribute non-holomorphic terms to quadratic gravitational couplings. It is then shown in the context of (2,2)-symmetric Z_N-orbifold theories that, for constant moduli backgrounds, the inclusion of such contributions can result in the cancellation of naked C"2-terms. R"2-terms can also arise but, being ghost free, need not cancel. (orig.)Available from TIB Hannover: RA 2999(94-224) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Non-perturbative monodromies in N=2 heterotic string vacua

We address non-perturbative effects and duality symmetries in N=2 heterotic string theories in four dimensions. Specifically, we consider how each of the four lines of enhanced gauge symmetries in the perturbative moduli space of N=2 T_2 compactifications is split into 2 lines where monopoles and dyons become massless. This amounts to considering non-perturbative effects originating from enhanced gauge symmetries at the microscopic string level. We show that the perturbative and non-perturbative monodromies consistently lead to the results of Seiberg-Witten upon identification of a consistent truncation procedure from local to rigid N=2 supersymmetry. (orig.)Available from TIB Hannover: RA 2999(95-150) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman