Instanton Effects in Matrix Models and String Effective Lagrangians

We perform an explicit calculation of the lowest order effects of single eigenvalue instantons on the continuous sector of the collective field theory derived from a $d=1$ bosonic matrix model. These effects consist of certain induced operators whose exact form we exhibit.Comment: Latex document, 36 pages, includes 6 figures appended as uuencoded eps files, preprint CERN-TH.7301/94, UPR-608

Area-scaling of quantum fluctuations

We show that fluctuations of bulk operators that are restricted to some region of space scale as the surface area of the region, independently of its geometry. Specifically, we consider two point functions of operators that are integrals over local operator densities whose two point functions falls off rapidly at large distances, and does not diverge too strongly at short distances. We show that the two point function of such bulk operators is proportional to the area of the common boundary of the two spatial regions. Consequences of this, relevant to the holographic principle and to area-scaling of Unruh radiation are briefly discussed.Comment: 20 pages, 5 figure

Duality in cosmological perturbation theory

Cosmological perturbation equations derived from low-energy effective actions are shown to be invariant under a duality transformation reminiscent of electric-magnetic, strong-weak coupling, S-duality. A manifestly duality-invariant approximation for perturbations far outside the horizon is introduced, and it is argued to be useful even during a high curvature epoch. Duality manifests itself through a remnant symmetry acting on the classical moduli of cosmological models, and implying lower bounds on the number and energy density of produced particles.Comment: 14 pages, LATEX, no figure

Dark Matter Axions in Models of String Cosmology

Axions are produced during a period of dilaton-driven inflation by amplification of quantum fluctuations. We show that for some range of string cosmology parameters and some range of axion masses, primordial axions may constitute a large fraction of the present energy density in the universe in the form of cold dark matter. Due to the periodic nature of the axion potential energy density fluctuations are strongly suppressed. The spectrum of primordial axions is not thermal, allowing a small fraction of the axions to remain relativistic until quite late.Comment: 11 pages, no figures, revte

The role of the superstring dilaton in cosmology and particle physics

Superstring theory predicts the existence of a scalar field, the dilaton. I review some basic features of the dilaton interactions and explain their possible consequences in cosmology and particle physics.Comment: Latex, 12 pages, preprint CERN-TH.7255/9

Causal Boundary Entropy From Horizon Conformal Field Theory

The quantum theory of near horizon regions of spacetimes with classical spatially flat, homogeneous and isotropic Friedman-Robertson-Walker geometry can be approximately described by a two dimensional conformal field theory. The central charge of this theory and expectation value of its Hamiltonian are both proportional to the horizon area in units of Newton's constant. The statistical entropy of horizon states, which can be calculated using two dimensional state counting methods, is proportional to the horizon area and depends on a numerical constant of order unity which is determined by Planck scale physics. This constant can be fixed such that the entropy is equal to a quarter of the horizon area in units of Newton's constant, in agreement with thermodynamic considerations.Comment: 11 pages, no figure

String Cosmology: An Update

A string cosmology scenario ("pre-big-bang") postulates that the evolution of the Universe starts from a state of very small curvature and coupling, undergoes a long phase of dilaton-driven kinetic inflation and at some later time joins smoothly standard radiation dominated cosmological evolution, thus giving rise to a singularity free inflationary cosmology. I report on recent progress in understanding some outstanding issues such as initial conditions, graceful exit transition and generation of inhomogeneity perturbations.Comment: 11 pages, 1 eps figure, Latex, based on talk at COSMO9