271 research outputs found
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-
Embeddings in Spacetimes Sourced by Scalar Fields
The extension of the Campbell-Magaard embedding theorem to general relativity
with minimally-coupled scalar fields is formulated and proven. The result is
applied to the case of a self-interacting scalar field for which new embeddings
are found, and to Brans-Dicke theory. The relationship between Campbell-Magaard
theorem and the general relativity, Cauchy and initial value problems is
outlined.Comment: RevTEX (11 pages)/ To appear in the Journal of Mathematical Physic
Symmetric vacuum scalar--tensor cosmology
The existence of point symmetries in the cosmological field equations of
generalized vacuum scalar--tensor theories is considered within the context of
the spatially homogeneous cosmologies. It is found that such symmetries only
occur in the Brans--Dicke theory when the dilaton field self--interacts.
Moreover, the interaction potential of the dilaton must take the form of a
cosmological constant. For the spatially flat, isotropic model, it is shown how
this point symmetry may be employed to generate a discrete scale factor duality
in the Brans--Dicke action.Comment: 10 pages, latex, To appear in Class. Quantum Gra
Supersymmetric Quantum Corrections and Poisson-Lie T-Duality
The quantum actions of the (4,4) supersymmetric non-linear sigma model and
its dual in the Abelian case are constructed by using the background superfield
method. The propagators of the quantum superfield and its dual and the gauge
fixing actions of the original and dual (4,4) supersymmetric sigma models are
determined. On the other hand, the BRST transformations are used to obtain the
quantum dual action of the (4,4) supersymmetric non-linear sigma model in the
sense of Poisson-Lie T-dualityComment: 18 page
Revisiting the calculations of inflationary perturbations
We present a new approximation scheme that allows us to increase the accuracy
of analytical predictions of the power spectra of inflationary perturbations
for two specific classes of inflationary models. Among these models are chaotic
inflation with a monomial potential, power-law inflation and natural inflation
(inflation at a maximum). After reviewing the established first order results
we calculate the amplitudes and spectral indices for these classes of models at
higher orders in the slow-roll parameters for scalar and tensorial
perturbations.Comment: Extended version of the talk to be published in the proceedings of
the Mexican Meeting on Exact Solutions and Scalar Fields in Gravity. Mexico,
1-6 October, 200
Dynamical study of the hyperextended scalar-tensor theory in the empty Bianchi type I model
The dynamics of the hyperextended scalar-tensor theory in the empty Bianchi
type I model is investigated. We describe a method giving the sign of the first
and second derivatives of the metric functions whatever the coupling function.
Hence, we can predict if a theory gives birth to expanding, contracting,
bouncing or inflationary cosmology. The dynamics of a string inspired theory
without antisymetric field strength is analysed. Some exact solutions are
found.Comment: 18 pages, 3 figure
The embedding of the spacetime in five-dimensional spaces with arbitrary non-degenerate Ricci tensor
We discuss and prove a theorem which asserts that any n-dimensional
semi-Riemannian manifold can be locally embedded in a (n+1)-dimensional space
with a non-degenerate Ricci tensor which is equal, up to a local analytic
diffeomorphism, to the Ricci tensor of an arbitrary specified space. This may
be regarded as a further extension of the Campbell-Magaard theorem. We
highlight the significance of embedding theorems of increasing degrees of
generality in the context of higher dimensional spacetimes theories and
illustrate the new theorem by establishing the embedding of a general class of
Ricci-flat spacetimes
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-
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