2,129 research outputs found
Cosmology and the S-matrix
We study conditions for the existence of asymptotic observables in cosmology.
With the exception of de Sitter space, the thermal properties of accelerating
universes permit arbitrarily long observations, and guarantee the production of
accessible states of arbitrarily large entropy. This suggests that some
asymptotic observables may exist, despite the presence of an event horizon.
Comparison with decelerating universes shows surprising similarities: Neither
type suffers from the limitations encountered in de Sitter space, such as
thermalization and boundedness of entropy. However, we argue that no realistic
cosmology permits the global observations associated with an S-matrix.Comment: 16 pages, 5 figures; v2: minor editin
Vacuum Energy Density for Massless Scalar Fields in Flat Homogeneous Spacetime Manifolds with Nontrivial Topology
Although the observed universe appears to be geometrically flat, it could
have one of 18 global topologies. A constant-time slice of the spacetime
manifold could be a torus, Mobius strip, Klein bottle, or others. This global
topology of the universe imposes boundary conditions on quantum fields and
affects the vacuum energy density via Casimir effect. In a spacetime with such
a nontrivial topology, the vacuum energy density is shifted from its value in a
simply-connected spacetime. In this paper, the vacuum expectation value of the
stress-energy tensor for a massless scalar field is calculated in all 17
multiply-connected, flat and homogeneous spacetimes with different global
topologies. It is found that the vacuum energy density is lowered relative to
the Minkowski vacuum level in all spacetimes and that the stress-energy tensor
becomes position-dependent in spacetimes that involve reflections and
rotations.Comment: 25 pages, 11 figure
Spacetime Structure of an Evaporating Black Hole in Quantum Gravity
The impact of the leading quantum gravity effects on the dynamics of the
Hawking evaporation process of a black hole is investigated. Its spacetime
structure is described by a renormalization group improved Vaidya metric. Its
event horizon, apparent horizon, and timelike limit surface are obtained taking
the scale dependence of Newton's constant into account. The emergence of a
quantum ergosphere is discussed. The final state of the evaporation process is
a cold, Planck size remnant.Comment: 23 pages, BibTeX, revtex4, 7 figure
Detection of acceleration radiation in a Bose-Einstein condensate
We propose and study methods for detecting the Unruh effect in a
Bose-Einstein condensate. The Bogoliubov vacuum of a Bose-Einstein condensate
is used here to simulate a scalar field-theory, and accelerated atom dots or
optical lattices as means for detecting phonon radiation due to acceleration
effects. We study Unruh's effect for linear acceleration and circular
acceleration. In particular, we study the dispersive effects of the Bogoliubov
spectrum on the ideal case of exact thermalization. Our results suggest that
Unruh's acceleration radiation can be tested using current accessible
experimental methods.Comment: 5 pages, 3 figure
Calculating the local-type fNL for slow-roll inflation with a non-vacuum initial state
Single-field slow-roll inflation with a non-vacuum initial state has an
enhanced bispectrum in the local limit. We numerically calculate the local-type
fNL signal in the CMB that would be measured for such models (including the
full transfer function and 2D projection). The nature of the result depends on
several parameters, including the occupation number N_k, the phase angle
\theta_k between the Bogoliubov parameters, and the slow-roll parameter
\epsilon. In the most conservative case, where one takes \theta_k \approx
\eta_0 k (justified by physical reasons discussed within) and \epsilon\lesssim
0.01, we find that 0 < fNL < 1.52 (\epsilon/0.01), which is likely too small to
be detected in the CMB. However, if one is willing to allow a constant value
for the phase angle \theta_k and N_k=O(1), fNL can be much larger and/or
negative (depending on the choice of \theta_k), e.g. fNL \approx 28
(\epsilon/0.01) or -6.4 (\epsilon/0.01); depending on \epsilon, these scenarios
could be detected by Planck or a future satellite. While we show that these
results are not actually a violation of the single-field consistency relation,
they do produce a value for fNL that is considerably larger than that usually
predicted from single-field inflation.Comment: 8 pages, 1 figure. v2: Version accepted for publication in PRD. Added
greatly expanded discussion of the phase angle \theta_k; this allows the
possibility of enhanced fNL, as mentioned in abstract. More explicit
comparisons with earlier wor
Hawking Radiation from Fluctuating Black Holes
Classically, black Holes have the rigid event horizon. However, quantum
mechanically, the event horizon of black holes becomes fuzzy due to quantum
fluctuations. We study Hawking radiation of a real scalar field from a
fluctuating black hole. To quantize metric perturbations, we derive the
quadratic action for those in the black hole background. Then, we calculate the
cubic interaction terms in the action for the scalar field. Using these
results, we obtain the spectrum of Hawking radiation in the presence of
interaction between the scalar field and the metric. It turns out that the
spectrum deviates from the Planck spectrum due to quantum fluctuations of the
metric.Comment: 35pages, 4 figure
Detecting many-body entanglements in noninteracting ultracold atomic fermi gases
We explore the possibility of detecting many-body entanglement using
time-of-flight (TOF) momentum correlations in ultracold atomic fermi gases. In
analogy to the vacuum correlations responsible for Bekenstein-Hawking black
hole entropy, a partitioned atomic gas will exhibit particle-hole correlations
responsible for entanglement entropy. The signature of these momentum
correlations might be detected by a sensitive TOF type experiment.Comment: 5 pages, 5 figures, fixed axes labels on figs. 3 and 5, added
reference
Fluctuation Spectrum from a Scalar-Tensor Bimetric Gravity Theory
Predictions of the CMB spectrum from a bimetric gravity theory
(gr-qc/0101126) are presented. The initial inflationary period in BGT is driven
by a vanishingly small speed of gravitational waves v_g in the very early
universe. This initial inflationary period is insensitive to the choice of
scalar field potential and initial values of the scalar field. After this
initial period of inflation, v_g will increase rapidly and the effects of a
potential will become important. We show that a quadratic potential introduced
into BGT yields an approximately flat spectrum with inflation parameters:
n_s=0.98, n_t=-0.027, alpha_s=-3.2e-4 and alpha_t=-5.0e-4, with r >= 0.014.Comment: 14 pages, uses amsmath, amssym
A model for time-dependent cosmological constant and its consistency with the present Friedmann universe
We use a model where the cosmological term can be related to the chiral gauge
anomaly of a possible quantum scenario of the initial evolution of the
universe. We show that this term is compatible with the Friedmann behavior of
the present universe.Comment: 5 pages, Revtex 4, twocolumn (minor corrections and improved
reference list. To appear in Classical and Quantum Gravity
Conformally related massless fields in dS, AdS and Minkowski spaces
In this paper we write down the equation for a scalar conformally coupled
field simultaneously for de Sitter (dS), anti-de Sitter (AdS) and Minkowski
spacetime in d-dimensions. The curvature dependence appears in a very simple
way through a conformal factor. As a consequence the process of curvature free
limit, including wave functions limit and two-points functions, turns to be a
straightforward issue. We determine a set of modes, that we call de Sitter
plane waves, which become ordinary plane waves when the curvature vanishes.Comment: 7 pages, 1 figur
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