950 research outputs found
Near-Horizon Virasoro Symmetry and the Entropy of de Sitter Space in Any Dimension
De Sitter spacetime is known to have a cosmological horizon that enjoys
thermodynamic-like properties similar to those of a black hole horizon. In this
note we show that a universal argument can be given for the entropy of de
Sitter spacetime in arbitrary dimensions, by generalizing a recent near horizon
symmetry plus conformal field theory argument of Carlip for black hole entropy.
The implications of this argument are also discussed.Comment: 13 pages, no figure. Add one reference and correct a minor typo in
pp.6, no change was made in tex
A terrestrial search for dark contents of the vacuum, such as dark energy, using atom interferometry
We describe the theory and first experimental work on our concept for
searching on earth for the presence of dark content of the vacuum (DCV) using
atom interferometry. Specifically, we have in mind any DCV that has not yet
been detected on a laboratory scale, but might manifest itself as dark energy
on the cosmological scale. The experimental method uses two atom
interferometers to cancel the effect of earth's gravity and diverse noise
sources. It depends upon two assumptions: first, that the DCV possesses some
space inhomogeneity in density, and second that it exerts a sufficiently strong
non-gravitational force on matter. The motion of the apparatus through the DCV
should then lead to an irregular variation in the detected matter-wave phase
shift. We discuss the nature of this signal and note the problem of
distinguishing it from instrumental noise. We also discuss the relation of our
experiment to what might be learned by studying the noise in gravitational wave
detectors such as LIGO.The paper concludes with a projection that a future
search of this nature might be carried out using an atom interferometer in an
orbiting satellite. The apparatus is now being constructed
The Cosmological Spacetime
We present here the transformations required to recast the Robertson-Walker
metric and Friedmann-Robertson-Walker equations in terms of observer-dependent
coordinates for several commonly assumed cosmologies. The overriding motivation
is the derivation of explicit expressions for the radius R_h of our cosmic
horizon in terms of measurable quantities for each of the cases we consider. We
show that the cosmological time dt diverges for any finite interval ds
associated with a process at R -> R_h, which therefore represents a physical
limit to our observations. This is a key component required for a complete
interpretation of the data, particularly as they pertain to the nature of dark
energy. With these results, we affirm the conclusion drawn in our earlier work
that the identification of dark energy as a cosmological constant does not
appear to be consistent with the data.Comment: Accepted for publication in the IJMP-D; 13 page
The Gravitational Horizon for a Universe with Phantom Energy
The Universe has a gravitational horizon, coincident with the Hubble sphere,
that plays an important role in how we interpret the cosmological data.
Recently, however, its significance as a true horizon has been called into
question, even for cosmologies with an equation-of-state w = p/rho > -1, where
p and rho are the total pressure and energy density, respectively. The claim
behind this argument is that its radius R_h does not constitute a limit to our
observability when the Universe contains phantom energy, i.e., when w < -1, as
if somehow that mitigates the relevance of R_h to the observations when w > -1.
In this paper, we reaffirm the role of R_h as the limit to how far we can see
sources in the cosmos, regardless of the Universe's equation of state, and
point out that claims to the contrary are simply based on an improper
interpretation of the null geodesics.Comment: 9 pages, 1 figure. Slight revisions in refereed version. Accepted for
publication in JCAP. arXiv admin note: text overlap with arXiv:1112.477
To the theory of the Universe evolution
Self-consistent account of the most simple non-gauge vector fields leads to a
broad spectrum of regular scenarios of temporal evolution of the Universe
completely within the frames of the Einstein's General relativity. The
longitudinal non-gauge vector field is "the missing link in the chain",
displaying the repulsive elasticity and allowing the macroscopic description of
the main features of the Universe evolution. The singular Big Bang turns into a
regular inflation-like state of maximum compression with the further
accelerated expansion at late times. The parametric freedom of the theory
allows to forget the troubles of fine tuning. In the most interesting cases the
analytical solutions of the Einstein's equations are found.Comment: 25 pages, 9figure
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