90 research outputs found
The Cosmological Constant Problem and Kaluza-Klein Theory
We present technical results which extend previous work and show that the
cosmological constant of general relativity is an artefact of the reduction to
4D of 5D Kaluza-Klein theory (or 10D superstrings and 11D supergravity). We
argue that the distinction between matter and vacuum is artificial in the
context of ND field theory. The concept of a cosmological ``constant'' (which
measures the energy density of the vacuum in 4D) should be replaced by that of
a series of variable fields whose sum is determined by a solution of ND field
equations in a well-defined manner.Comment: 11 pages, no figures, Latex. Accepted by Int. J. Mod. Phys.
Possible Wormhole Solutions in (4+1) Gravity
We extend previous analyses of soliton solutions in (4+1) gravity to new
ranges of their defining parameters. The geometry, as studied using invariants,
has the topology of wormholes found in (3+1) gravity. In the induced-matter
picture, the fluid does not satisfy the strong energy conditions, but its
gravitational mass is positive. We infer the possible existance of (4+1)
wormholes which, compared to their (3+1) counterparts, are less exotic.Comment: 3 pages, latex, 1 figure
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
Qualitative Analysis of Isotropic Curvature String Cosmologies
A complete qualitative study of the dynamics of string cosmologies is
presented for the class of isotopic curvature universes. These models are of
Bianchi types I, V and IX and reduce to the general class of
Friedmann-Robertson-Walker universes in the limit of vanishing shear isotropy.
A non-trivial two-form potential and cosmological constant terms are included
in the system. In general, the two-form potential and spatial curvature terms
are only dynamically important at intermediate stages of the evolution. In many
of the models, the cosmological constant is important asymptotically and
anisotropy becomes dynamically negligible. There also exist bouncing
cosmologies.Comment: Accepted to Classical and Quantum Gravity, 40 pages, 12 figures (uses
"graphicx" package for figures
Induced Matter and Particle Motion in Non-Compact Kaluza-Klein Gravity
We examine generalizations of the five-dimensional canonical metric by
including a dependence of the extra coordinate in the four-dimensional metric.
We discuss a more appropriate way to interpret the four-dimensional
energy-momentum tensor induced from the five-dimensional space-time and show it
can lead to quite different physical situations depending on the interpretation
chosen. Furthermore, we show that the assumption of five-dimensional null
trajectories in Kaluza-Klein gravity can correspond to either four-dimensional
massive or null trajectories when the path parameterization is chosen properly.
Retaining the extra-coordinate dependence in the metric, we show the
possibility of a cosmological variation in the rest masses of particles and a
consequent departure from four-dimensional geodesic motion by a geometric
force. In the examples given, we show that at late times it is possible for
particles traveling along 5D null geodesics to be in a frame consistent with
the induced matter scenario.Comment: 29 pages, accepted to GR
Scalar Field Cosmologies with Barotropic Matter: Models of Bianchi class B
We investigate in detail the qualitative behaviour of the class of Bianchi
type B spatially homogeneous cosmological models in which the matter content is
composed of two non-interacting components; the first component is described by
a barotropic fluid having a gamma-law equation of state, whilst the second is a
non-interacting scalar field (phi) with an exponential potential V=Lambda exp(k
phi). In particular, we study the asymptotic properties of the models both at
early and late times, paying particular attention on whether the models
isotropize (and inflate) to the future, and we discuss the genericity of the
cosmological scaling solutions.Comment: 18 pages, 1 figure, uses revtex and epsf to insert figur
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