487 research outputs found
Low-energy quantum string cosmology
We introduce a Wheeler-De Witt approach to quantum cosmology based on the
low-energy string effective action, with an effective dilaton potential
included to account for non-perturbative effects and, possibly, higher-order
corrections. We classify, in particular, four different classes of scattering
processes in minisuperspace, and discuss their relevance for the solution of
the graceful exit problem.Comment: Extended version to appear in the Review section of Int. J. Theor.
Phys. A 13 (1998). The new permanent address is added. An updated collection
of papers on the pre-big bang scenario is available at
http://www.to.infn.it/~gasperi
Qualitative Analysis of Early Universe Cosmologies
A qualitative analysis is presented for a class of homogeneous cosmologies
derived from the string effective action when a cosmological constant is
present in the matter sector of the theory. Such a term has significant effects
on the qualitative dynamics. For example, models exist which undergo a series
of oscillations between expanding and contracting phases due to the existence
of a heteroclinic cycle in the phase space. Particular analytical solutions
corresponding to the equilibrium points are also found.Comment: Submitted to Journal of Mathematical Physics, 18 pages, 4 figures,
uses package "graphicx" to insert figure
Study of orbiter/payload interface communications configuration control board directive from an operational perspective
Orbiter/payload data and communications interface was examined. It was found that the Configuration Control Board Directive (CCBD) greatly increases the capability of the orbiter to communicate with a wide variety of projected shuttle payloads. Rather than being derived from individual payload communication requirements, the CCBD appears to be based on an operational philosophy that requires the orbiter to duplicate or augment the ground network/payload communication links. It is suggested that the implementation of the CCBD be reviewed and compared with the Level 1 Program Requirements Document, differences reconciled, and interface characteristics defined
The Andante Regime of Scalar Field Dynamics
The andante regime of scalar field dynamics in the chaotic inflationary
Universe is defined as the epoch when the field is rolling moderately slowly
down its interaction potential, but at such a rate that first-order corrections
to the slow-roll approximation become important. These conditions should apply
towards the end of inflation as the field approaches the global minimum of the
potential. Solutions to the Einstein-scalar field equations for the class of
power law potentials are found in this regime in
terms of the inverse error function.Comment: 11 pages of plain Latex, FNAL-Pub-94/226-
Supersymmetric Quantization of Anisotropic Scalar-Tensor Cosmologies
In this paper we show that the spatially homogeneous Bianchi type I and
Kantowski-Sachs cosmologies derived from the Brans-Dicke theory of gravity
admit a supersymmetric extension at the quantum level. Global symmetries in the
effective one-dimensional actions characterize both classical and quantum
solutions. A wide family of exact wavefunctions satisfying the supersymmetric
constraints are found. A connection with quantum wormholes is briefly
discussed.Comment: In Press, Class. Quantum Grav. 20 pages, Late
Observing the Inflaton Potential
We show how observations of the density perturbation (scalar) spectrum and
the gravitational wave (tensor) spectrum allow a reconstruction of the
potential responsible for cosmological inflation. A complete functional
reconstruction or a perturbative approximation about a single scale are
possible; the suitability of each approach depends on the data available.
Consistency equations between the scalar and tensor spectra are derived, which
provide a powerful signal of inflation.Comment: 9 pages, LaTeX, FERMILAB--PUB--93/071--A; SUSSEX-AST 93/4-
Strings at future singularities
We discuss the behaviour of strings propagating in spacetimes which allow
future singularities of either a sudden future or a Big-Rip type. We show that
in general the invariant string size remains finite at sudden future
singularities while it grows to infinity at a Big-Rip. This claim is based on
the discussion of both the tensile and null strings. In conclusion, strings may
survive a sudden future singularity, but not a Big-Rip where they are
infinitely stretched.Comment: REVTEX 4.0, 4 pages, no figures, references adde
- …