2,268 research outputs found
Weak field limit of Reissner-Nordstrom black hole lensing
We study gravitational lensing by a Reissner-Nordstrom (RN) black hole in the
weak field limit. We obtain the basic equations for the deflection angle and
time delay and find analytical expressions for the positions and amplifications
of the primary and secondary images. Due to a net positive charge, the
separation between images increases, but no change in the total magnification
occurs.Comment: 8 pages, to appear in Phys. Rev.
Cosmological constraints for the Cosmic Defect theory
The Cosmic Defect theory has been confronted with four observational
constraints: primordial nuclear species abundances emerging from the big bang
nucleosynthesis; large scale structure formation in the universe; cosmic
microwave background acoustic scale; luminosity distances of type Ia
supernovae. The test has been based on a statistical analysis of the a
posteriori probabilities for three parameters of the theory. The result has
been quite satisfactory and such that the performance of the theory is not
distinguishable from the one of the Lambda-CDM theory. The use of the optimal
values of the parameters for the calculation of the Hubble constant and the age
of the universe confirms the compatibility of the Cosmic Defect approach with
observations.Comment: 13 pages, 1 figure, in press on IJMP
Spherical symmetry in a dark energy permeated space-time
The properties of a spherically symmetric static space-time permeated of dark
energy are worked out. Dark energy is viewed as the strain energy of an
elastically deformable four dimensional manifold. The metric is worked out in
the vacuum region around a central spherical mass/defect in the linear
approximation. We discuss analogies and differences with the analogue in the de
Sitter space time and how these competing scenarios could be differentiated on
an observational ground. The comparison with the tests at the solar system
scale puts upper limits to the parameters of the theory, consistent with the
values obtained applying the classical cosmological tests.Comment: 14 pages, 1 figure, in press on Classical and Quantum Gravit
Cosmography with strong lensing of LISA gravitational wave sources
LISA might detect gravitational waves from mergers of massive black hole
binaries strongly lensed by intervening galaxies (Sereno et al. 2010). The
detection of multiple gravitational lensing events would provide a new tool for
cosmography. Constraints on cosmological parameters could be placed by
exploiting either lensing statistics of strongly lensed sources or time delay
measurements of lensed gravitational wave signals. These lensing methods do not
need the measurement of the redshifts of the sources and the identification of
their electromagnetic counterparts. They would extend cosmological probes to
redshift z <= 10 and are then complementary to other lower or higher redshift
tests, such as type Ia supernovae or cosmic microwave background. The accuracy
of lensing tests strongly depends on the formation history of the merging
binaries, and the related number of total detectable multiple images. Lensing
amplification might also help to find the host galaxies. Any measurement of the
source redshifts would allow to exploit the distance-redshift test in
combination with lensing methods. Time-delay analyses might measure the Hubble
parameter H_0 with accuracy of >= 10 km s^{-1}Mpc^{-1}. With prior knowledge of
H_0, lensing statistics and time delays might constrain the dark matter density
(delta Omega_M >= 0.08, due to parameter degeneracy). Inclusion of our methods
with other available orthogonal techniques might significantly reduce the
uncertainty contours for Omega_M and the dark energy equation of state.Comment: 10 pages, 10 figures, in press on MNRA
Imprints of deviations from the gravitational inverse-square law on the power spectrum of mass fluctuations
Deviations from the gravitational inverse-square law would imprint
scale-dependent features on the power spectrum of mass density fluctuations. We
model such deviations as a Yukawa-like contribution to the gravitational
potential and discuss the growth function in a mixed dark matter model with
adiabatic initial conditions. Evolution of perturbations is considered in
general non-flat cosmological models with a cosmological constant, and an
analytical approximation for the growth function is provided. The coupling
between baryons and cold dark matter across recombination is negligibly
affected by modified gravity physics if the proper cutoff length of the
long-range Yukawa-like force is > 10 h^{-1} Mpc. Enhancement of gravity affects
the subsequent evolution, boosting large-scale power in a way that resembles
the effect of a lower matter density. This phenomenon is almost perfectly
degenerate in power-spectrum shape with the effect of a background of massive
neutrinos. Back-reaction on density growth from a modified cosmic expansion
rate should however also affect the normalization of the power spectrum, with a
shape distortion similar to the case of a non-modified background.Comment: 8 pages, 7 figures; submitted to MNRA
In vivo functional and myeloarchitectonic mapping of human primary auditory areas
In contrast to vision, where retinotopic mapping alone can define areal borders, primary auditory areas such as A1 are best delineated by combining in vivo tonotopic mapping with postmortem cyto- or myeloarchitectonics from the same individual. We combined high-resolution (800 Îźm) quantitative T(1) mapping with phase-encoded tonotopic methods to map primary auditory areas (A1 and R) within the "auditory core" of human volunteers. We first quantitatively characterize the highly myelinated auditory core in terms of shape, area, cortical depth profile, and position, with our data showing considerable correspondence to postmortem myeloarchitectonic studies, both in cross-participant averages and in individuals. The core region contains two "mirror-image" tonotopic maps oriented along the same axis as observed in macaque and owl monkey. We suggest that these two maps within the core are the human analogs of primate auditory areas A1 and R. The core occupies a much smaller portion of tonotopically organized cortex on the superior temporal plane and gyrus than is generally supposed. The multimodal approach to defining the auditory core will facilitate investigations of structure-function relationships, comparative neuroanatomical studies, and promises new biomarkers for diagnosis and clinical studies
On lensing by a cosmological constant
Several recent papers have suggested that the cosmological constant Lambda
directly influences the gravitational deflection of light. We place this
problem in a cosmological context, deriving an expression for the linear
potentials which control the cosmological bending of light, finding that it has
no explicit dependence on the cosmological constant. To explore the physical
origins of the apparent Lambda-dependent potential that appears in the static
Kottler metric, we highlight the two classical effects which lead to the
aberration of light. The first relates to the observer's motion relative to the
source, and encapsulates the familiar concept of angular-diameter distance. The
second term, which has proved to be the source of debate, arises from cosmic
acceleration, but is rarely considered since it vanishes for photons with
radial motion. This apparent form of light-bending gives the appearance of
curved geodesics even within a flat and homogeneous universe. However this
cannot be construed as a real lensing effect, since its value depends on the
observer's frame of reference. Our conclusion is thus that standard results for
gravitational lensing in a universe containing Lambda do not require
modification, with any influence of Lambda being restricted to negligible
high-order terms.Comment: 10 pages, 6 figures. Added new Section 3 and Figures 1,2,5. To appear
in MNRA
Imprints of deviations from the gravitational inverse-square law on the power spectrum of mass fluctuations
Deviations from the gravitational inverse-square law would imprint scale-dependent features on the power spectrum of mass density fluctuations. We model such deviations as a Yukawa-like contribution to the gravitational potential and discuss the growth function in a mixed dark matter model with adiabatic initial conditions. Evolution of perturbations is considered in general non-flat cosmological models with a cosmological constant, and an analytical approximation for the growth function is provided. The coupling between baryons and cold dark matter across recombination is negligibly affected by modified gravity physics if the proper cut-off length of the long-range Yukawa-like force is âł10âhâ1âMpc. Enhancement of gravity affects the subsequent evolution, boosting large-scale power in a way that resembles the effect of a lower matter density. This phenomenon is almost perfectly degenerate in power-spectrum shape with the effect of a background of massive neutrinos. Back-reaction on density growth from a modified cosmic expansion rate should, however, also affect the normalization of the power spectrum, with a shape distortion similar to the case of a non-modified backgroun
Offensive jokes: How do they impact long-term relationships?
This is the publisher's version, also available electronically from http://www.degruyter.com/view/j/humr.2010.23.issue-3/humr.2010.016/humr.2010.016.xml.This article explores the impact of the use of negative humor on relational satisfaction and the importance of humor in long-term relationships from a coorientation perspective. Dyadic data from 123 couples were gathered using a survey measuring positive and negative humor use. These data were analyzed using structural equations modeling and the Actor-Partner Independence Model (Kenny et al., Dyadic data analysis, The Guilford Press, 2006: 144). Negative humor weakly predicted relational outcomes, but was valuable when partners saw themselves as possessing a shared sense of humor. Men acknowledge that their own public negative humor use negatively impacts the importance of humor in their relationship. Perceived similarity in negative humor use positively predicts relational satisfaction for both partners, and positively predicts the importance of humor for men, regardless of how much positive humor the couple uses. Accurately knowing a partner's negative humor use, or having greater understanding, negatively predicted relational outcomes
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