82 research outputs found
Can Gravitational Waves Prevent Inflation?
To investigate the cosmic no hair conjecture, we analyze numerically
1-dimensional plane symmetrical inhomogeneities due to gravitational waves in
vacuum spacetimes with a positive cosmological constant. Assuming periodic
gravitational pulse waves initially, we study the time evolution of those waves
and the nature of their collisions. As measures of inhomogeneity on each
hypersurface, we use the 3-dimensional Riemann invariant and the electric and magnetic parts of
the Weyl tensor. We find a temporal growth of the curvature in the waves'
collision region, but the overall expansion of the universe later overcomes
this effect. No singularity appears and the result is a ``no hair" de Sitter
spacetime. The waves we study have amplitudes between and widths between ,
where , the horizon scale of de Sitter spacetime. This
supports the cosmic no hair conjecture.Comment: LaTeX, 11 pages, 3 figures are available on request <To
[email protected] (Hisa-aki SHINKAI)>, WU-AP/29/9
Inflationary Initial Conditions Consistent with Causality
The initial condition problem of inflation is examined from the perspective
of both spacetime embedding and scalar field dynamics. The spacetime embedding
problem is solved for arbitrary initial spatial curvature Omega, which
generalizes previous works that primarily treat the flat case Omega=1. Scalar
field dynamics that is consistent with the embedding constraints are examined,
with the additional treatment of damping effects. The effects of
inhomogeneities on the embedding problem also are considered. A category of
initial conditions are identified that are not acausal and can develop into an
inflationary regime.Comment: 9 pages, 3 figures. Minor changes, matches version to appear in
Physical Review
Semiclassical Effects and the Onset of Inflation
We present a class of exact solutions to the constraint equations of General
Relativity coupled to a Klein - Gordon field, these solutions being isotropic
but not homogeneous. We analyze the subsequent evolution of the consistent
Cauchy data represented by those solutions, showing that only certain special
initial conditions eventually lead to successfull Inflationary cosmologies. We
argue, however, that these initial conditions are precisely the likely outcomes
of quantum events occurred before the inflationary era.Comment: 22 pages, file written in RevTe
Modeling Collisionless Matter in General Relativity: A New Numerical Technique
We propose a new numerical technique for following the evolution of a
self-gravitating collisionless system in general relativity. Matter is modeled
as a scalar field obeying the coupled Klein-Gordon and Einstein equations. A
phase space distribution function, constructed using covariant coherent states,
obeys the relativistic Vlasov equation provided the de Broglie wavelength for
the field is very much smaller than the scales of interest. We illustrate the
method by solving for the evolution of a system of particles in a static,
plane-symmetric, background spacetime.Comment: 6 pages, 3 postscript figures, submitted to Physical Review
Spherically Symmetric Inflation
It is shown in this letter that in the framework of an inhomogeneous geometry
and a massive non self-interacting scalar field with spherical symmetry, one
needs a homogeneous patch bigger than a dizaine of horizons in order to start
inflation. The results are completly independent of initial conditions on the
spatial distribution of the scalar field. The initial condition on the metric
parameters are also justified. This is a generalization of the results obtained
in Ref.[1], showing that their conclusions are rather robust.Comment: Latex file, 4 pages, no figure
Scaling of curvature in sub-critical gravitational collapse
We perform numerical simulations of the gravitational collapse of a
spherically symmetric scalar field. For those data that just barely do not form
black holes we find the maximum curvature at the position of the central
observer. We find a scaling relation between this maximum curvature and
distance from the critical solution. The scaling relation is analogous to that
found by Choptuik for black hole mass for those data that do collapse to form
black holes. We also find a periodic wiggle in the scaling exponent.Comment: Revtex, 2 figures, Discussion modified, to appear in Phys. Rev.
Galerkin Method in the Gravitational Collapse: a Dynamical System Approach
We study the general dynamics of the spherically symmetric gravitational
collapse of a massless scalar field. We apply the Galerkin projection method to
transform a system of partial differential equations into a set of ordinary
differential equations for modal coefficients, after a convenient truncation
procedure, largely applied to problems of turbulence. In the present case, we
have generated a finite dynamical system that reproduces the essential features
of the dynamics of the gravitational collapse, even for a lower order of
truncation. Each initial condition in the space of modal coefficients
corresponds to a well definite spatial distribution of scalar field. Numerical
experiments with the dynamical system show that depending on the strength of
the scalar field packet, the formation of black-holes or the dispersion of the
scalar field leaving behind flat spacetime are the two main outcomes. We also
found numerical evidence that between both asymptotic states, there is a
critical solution represented by a limit cycle in the modal space with period
.Comment: 9 pages, revtex4, 10 ps figures; Phys. Rev. D, in pres
Two Boosted Black Holes in Asymptotically de Sitter Space-Time - Relation between Mass and Apparent Horizon Formation -
We study the apparent horizon for two boosted black holes in the
asymptotically de Sitter space-time by solving the initial data on a space with
punctures. We show that the apparent horizon enclosing both black holes is not
formed if the conserved mass of the system (Abbott-Deser mass) is larger than a
critical mass. The black hole with too large AD mass therefore cannot be formed
in the asymptotically de Sitter space-time even though each black hole has any
inward momentum. We also discuss the dynamical meaning of AD mass by examining
the electric part of the Weyl tensor (the tidal force) for various initial
data.Comment: 15 pages, accepted for publication in PR
Numerical Study of Inhomogeneous Pre-Big-Bang Inflationary Cosmology
We study numerically the inhomogeneous pre-big-bang inflation in a
spherically symmetric space-time. We find that a large initial inhomogeneity
suppresses the onset of the pre-big-bang inflation. We also find that even if
the pre-big-bang inflationary stage is realized, the initial inhomogeneities
are not homogenized. Namely, during the pre-big-bang inflation
``hairs''(irregularities) do not fall, in sharp contrast to the usual
(potential energy dominated) inflation where initial inhomogeneity and
anisotropy are damped and thus the resulting universe is less sensitive to
initial conditions.Comment: 12 pages + 14 figures, to be published in Phys.Rev.
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