182 research outputs found
Deuteronomy and Numbers
Four light isotopes - D, ^3He, ^4He and ^7Li - were produced by nuclear
reactions a few seconds after the big bang. New measurements of ^3He in the ISM
by Gloeckler and Geiss and of deuterium in high redshift hydrogen clouds by
Tytler and his collaborators provide further confirmation of big-bang
nucleosynthesis and new insight about the density of ordinary matter (baryons).Comment: 6 pages LaTeX with 1 eps Figur
How Sensitive is the CMB to a Single Lens?
We study the imprints of a single lens, that breaks statistical isotropy, on
the CMB and calculate the signal to noise ratio (S/N) for its detection. We
emphasize the role of non-Gaussianities induced by LCDM weak lensing in this
calculation and show that typically the S/N is much smaller than expected. In
particular we find that the hypothesis that a void (texture) is responsible for
the WMAP cold spot can barely (cannot) be tested via weak lensing of the CMB.Comment: Accepted for publication in JCAP, 24 pages, 5 figure
Consistency of the Shannon entropy in quantum experiments
The consistency of the Shannon entropy, when applied to outcomes of quantum
experiments, is analysed. It is shown that the Shannon entropy is fully
consistent and its properties are never violated in quantum settings, but
attention must be paid to logical and experimental contexts. This last remark
is shown to apply regardless of the quantum or classical nature of the
experiments.Comment: 12 pages, LaTeX2e/REVTeX4. V5: slightly different than the published
versio
Scalar-Tensor Gravity and Quintessence
Scalar fields with inverse power-law effective potentials may provide a
negative pressure component to the energy density of the universe today, as
required by cosmological observations. In order to be cosmologically relevant
today, the scalar field should have a mass
, thus potentially inducing sizable
violations of the equivalence principle and space-time variations of the
coupling constants. Scalar-tensor theories of gravity provide a framework for
accommodating phenomenologically acceptable ultra-light scalar fields. We
discuss non-minimally coupled scalar-tensor theories in which the scalar-matter
coupling is a dynamical quantity. Two attractor mechanisms are operative at the
same time: one towards the tracker solution, which accounts for the accelerated
expansion of the Universe, and one towards general relativity, which makes the
ultra-light scalar field phenomenologically safe today. As in usual
tracker-field models, the late-time behavior is largely independent on the
initial conditions. Strong distortions in the cosmic microwave background
anisotropy spectra as well as in the matter power spectrum are expected.Comment: 5 pages, 4 figure
Ellipsoidal universe in the brane world
We study a scenario of the ellipsoidal universe in the brane world cosmology
with a cosmological constant in the bulk . From the five-dimensional Einstein
equations we derive the evolution equations for the eccentricity and the scale
factor of the universe, which are coupled to each other. It is found that if
the anisotropy of our universe is originated from a uniform magnetic field
inside the brane, the eccentricity decays faster in the bulk in comparison with
a four-dimensional ellipsoidal universe. We also investigate the ellipsoidal
universe in the brane-induced gravity and find the evolution equation for the
eccentricity which has a contribution determined by the four- and
five-dimensional Newton's constants. The role of the eccentricity is discussed
in explaining the quadrupole problem of the cosmic microwave background.Comment: 15 pages, 1 figure, Version 3, references added, contents expande
Cosmic Acceleration Driven by Mirage Inhomogeneities
A cosmological model based on an inhomogeneous D3-brane moving in an AdS_5 X
S_5 bulk is introduced. Although there is no special points in the bulk, the
brane Universe has a center and is isotropic around it. The model has an
accelerating expansion and its effective cosmological constant is inversely
proportional to the distance from the center, giving a possible geometrical
origin for the smallness of a present-day cosmological constant. Besides, if
our model is considered as an alternative of early time acceleration, it is
shown that the early stage accelerating phase ends in a dust dominated FRW
homogeneous Universe. Mirage-driven acceleration thus provides a dark matter
component for the brane Universe final state. We finally show that the model
fulfills the current constraints on inhomogeneities.Comment: 14 pages, 1 figure, IOP style. v2, changed style, minor corrections,
references added, version accepted in Class. Quant. Gra
The parent analogy: a reassessment
According to the parent analogy, as a caretaker’s goodness, ability and intelligence increase, the likelihood that the caretaker will make arrangements for the attainment of future goods that are unnoticed or underappreciated by their dependents also increases. Consequently, if this analogy accurately represents our relationship to God, then we should expect to find many instances of inscrutable evil in the world. This argument in support of skeptical theism has recently been criticized by Dougherty. I argue that Dougherty’s argument is incomplete, for there are two plausible ways of construing the parent analogy’s conclusion. I supplement Dougherty’s case by offering a new argument against the parent analogy based on failed expectations concerning the amount of inscrutable evils encountered in the world. Consequently, there remains a significant empirical hurdle for skeptical theism to overcome if it is to maintain its status as a defeater for our reliability when tracking gratuitous evils.Publisher PDFPeer reviewe
Solar Wakes of Dark Matter Flows
We analyze the effect of the Sun's gravitational field on a flow of cold dark
matter (CDM) through the solar system in the limit where the velocity
dispersion of the flow vanishes. The exact density and velocity distributions
are derived in the case where the Sun is a point mass. The results are extended
to the more realistic case where the Sun has a finite size spherically
symmetric mass distribution. We find that regions of infinite density, called
caustics, appear. One such region is a line caustic on the axis of symmetry,
downstream from the Sun, where the flow trajectories cross. Another is a
cone-shaped caustic surface near the trajectories of maximum scattering angle.
The trajectories forming the conical caustic pass through the Sun's interior
and probe the solar mass distribution, raising the possibility that the solar
mass distribution may some day be measured by a dark matter detector on Earth.
We generalize our results to the case of flows with continuous velocity
distributions, such as that predicted by the isothermal model of the Milky Way
halo.Comment: 30 pages, 8 figure
On the Detection of a Scalar Stochastic Background of Gravitational Waves
In the near future we will witness the coming to a full operational regime of
laser interferometers and resonant mass detectors of spherical shape. In this
work we study the sensitivity of pairs of such gravitational wave detectors to
a scalar stochastic background of gravitational waves. Our computations are
carried out both for minimal and non minimal coupling of the scalar fields.Comment: 25 pages, 3 figure
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