25 research outputs found
Cosmic Crystallography with a Pullback
We present a modified version of the cosmic crystallography method,
especially useful for testing closed models of negative spatial curvature. The
images of clusters of galaxies in simulated catalogs are ``pulled back'' to the
fundamental domain before the set of distances is calculated.Comment: 9 pages, 2 figure
Casimir energy density in closed hyperbolic universes
The original Casimir effect results from the difference in the vacuum
energies of the electromagnetic field, between that in a region of space with
boundary conditions and that in the same region without boundary conditions. In
this paper we develop the theory of a similar situation, involving a scalar
field in spacetimes with compact spatial sections of negative spatial
curvature.Comment: 10 pages. Contribution to the "Fifth Alexander Friedmann
International Seminar on Gravitation and Cosmology," Joao Pessoa, Brazil,
2002. Revised version, with altered Abstract and one new referenc
On Closed Einstein-de Sitter Universes
We briefly summarize the idea of cosmological models with compact, flat
spatial sections. It has been suggested that, because of the COBE satellite's
maps of the microwave background, such models cannot be small in the sense of
Ellis, and hence are no longer interesting. Here we use Lehoucq et al.'s method
of cosmic crystallography to show that these models are physically meaningful
even if the size of the spatial sections is of the same order of magnitude as
the radius of the observational horizon.Comment: 8 pages, 1 figure. Revision includes comment on "top-down" and
"bottom-up" pictures of structure formation. Figure is unmodifie
Casimir energy in a small volume multiply connected static hyperbolic pre-inflationary Universe
A few years ago, Cornish, Spergel and Starkman (CSS), suggested that a
multiply connected ``small'' Universe could allow for classical chaotic mixing
as a pre-inflationary homogenization process. The smaller the volume, the more
important the process. Also, a smaller Universe has a greater probability of
being spontaneously created. Previously DeWitt, Hart and Isham (DHI) calculated
the Casimir energy for static multiply connected flat space-times. Due to the
interest in small volume hyperbolic Universes (e.g. CSS), we generalize the DHI
calculation by making a a numerical investigation of the Casimir energy for a
conformally coupled, massive scalar field in a static Universe, whose spatial
sections are the Weeks manifold, the smallest Universe of negative curvature
known. In spite of being a numerical calculation, our result is in fact exact.
It is shown that there is spontaneous vacuum excitation of low multipolar
components.Comment: accepted for publication in phys. rev.