The Experts below are selected from a list of 24924 Experts worldwide ranked by ideXlab platform
Uros Seljak - One of the best experts on this subject based on the ideXlab platform.
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Gravitational Lensing effect on cosmic microwave background polarization
Physical Review D, 1998Co-Authors: Matias Zaldarriaga, Uros SeljakAbstract:We investigate the effect of Gravitational Lensing by matter distribution in the universe on the cosmic microwave background polarization power spectra and temperature-polarization cross-correlation spectrum. As in the case of the temperature spectrum, Gravitational Lensing leads to a smoothing of narrow features and the enhancement of power on the damping tail of the power spectrum. Because the acoustic peaks in polarization spectra are narrower than in the temperature spectrum the smoothing effect is significantly larger and can reach up to 10% for $ll1000$ and even more above that. A qualitatively new feature is the generation of $B$ type polarization even when only $E$ is intrinsically present, such as in the case of pure scalar perturbations. This may be directly observed with Planck and other future small scale polarization experiments. The Gravitational Lensing effect is incorporated in the new version (2.4) of the CMBFAST code.
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Gravitational Lensing effect on cosmic microwave background anisotropies a power spectrum approach
The Astrophysical Journal, 1996Co-Authors: Uros SeljakAbstract:The effect of Gravitational Lensing on cosmic microwave background (CMB) anisotropies is investigated using the power spectrum approach. The Lensing effect can be calculated in any cosmological model by specifying the evolution of Gravitational potential. Previous work on this subject is generalized to a non-flat universe and to a nonlinear evolution regime. Gravitational Lensing cannot change the gross distribution of CMB anisotropies, but it may redistribute the power and smooth the sharp features in the CMB power spectrum. The magnitude of this effect is estimated using observational constraints on the power spectrum of Gravitational potential from galaxy and cluster surveys and also using the limits on correlated ellipticities in distant galaxies. For realistic CMB power spectra the effect on CMB multipole moments is less then a few percent on degree angular scales, but gradually increases towards smaller scales. On arcminute angular scales the acoustic oscillation peaks may be partially or completely smoothed out because of the Gravitational Lensing.
Mark Wyman - One of the best experts on this subject based on the ideXlab platform.
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galilean invariant scalar fields can strengthen Gravitational Lensing
Physical Review Letters, 2011Co-Authors: Mark WymanAbstract:: The mystery of dark energy suggests that there is new Gravitational physics on long length scales. Yet light degrees of freedom in gravity are strictly limited by Solar System observations. We can resolve this apparent contradiction by adding a Galilean-invariant scalar field to gravity. Called Galileons, these scalars have strong self-interactions near overdensities, like the Solar System, that suppress their dynamical effect. These nonlinearities are weak on cosmological scales, permitting new physics to operate. In this Letter, we point out that a massive-gravity-inspired coupling of Galileons to stress energy can enhance Gravitational Lensing. Because the enhancement appears at a fixed scaled location for dark matter halos of a wide range of masses, stacked cluster analysis of weak Lensing data should be able to detect or constrain this effect.
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galilean invariant scalar fields can strengthen Gravitational Lensing
Physical Review Letters, 2011Co-Authors: Mark WymanAbstract:The mystery of dark energy suggests that there is new Gravitational physics on long length scales. Yet light degrees of freedom in gravity are strictly limited by Solar System observations. We can resolve this apparent contradiction by adding a Galilean-invariant scalar field to gravity. Called Galileons, these scalars have strong self-interactions near overdensities, like the Solar System, that suppress their dynamical effect. These nonlinearities are weak on cosmological scales, permitting new physics to operate. In this Letter, we point out that a massive gravity inspired coupling of Galileons to stress energy gravity can have a surprising consequence: enhanced Gravitational Lensing. Because the enhancement appears at a fixed scaled location for a wide range of dark matter halo masses, stacked cluster analysis of weak Lensing data should be able to detect or constrain this effect.
Matthias Bartelmann - One of the best experts on this subject based on the ideXlab platform.
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Weak Gravitational Lensing
Physics Reports, 2020Co-Authors: Matthias Bartelmann, Peter SchneiderAbstract:We review theory and applications of weak Gravitational Lensing. After summarising Friedmann-Lemaitre cosmological models, we present the formalism of Gravitational Lensing and light propagation in arbitrary space-times. We discuss how weak-Lensing effects can be measured. The formalism is then applied to reconstructions of galaxy-cluster mass distributions, Gravitational Lensing by large-scale matter distributions, QSO-galaxy correlations induced by weak Lensing, Lensing of galaxies by galaxies, and weak Lensing of the cosmic microwave background. Contents: Introduction - Cosmological Background - Gravitational Light Deflection - Principles of Weak Gravitational Lensing - Weak Lensing by Galaxy Clusters - Weak Cosmological Lensing - QSO Magnification Bias and Large-Scale Structure - Galaxy-Galaxy Lensing - The Impact of Weak Gravitational Lensing on the Microwave Background Radiation - Summary and OutlookComment: Review; 223 pages; figures embedded; to be submitted to Physics Reports; constructive comments are invite
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Applications of Gravitational Lensing in Cosmology
Springer Praxis Books, 2020Co-Authors: Matthias BartelmannAbstract:Gravitational Lensing originates from the deflection of light by masses, irrespective of their physical state or composition. Since it appears inescapable that most of the matter in the universe is dark, Gravitational Lensing has developed into one of the primary tools to learn about the amount, composition and distribution of masses in the universe.
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Masses of Galaxy Clusters from Gravitational Lensing
Space Science Reviews, 2013Co-Authors: Henk Hoekstra, Matthias Bartelmann, Håkon Dahle, Holger Israel, Marceau Limousin, Massimo MeneghettiAbstract:Despite consistent progress in numerical simulations, the observable properties of galaxy clusters are difficult to predict ab initio. It is therefore important to compare both theoretical and observational results to a direct measure of the cluster mass. This can be done by measuring the Gravitational Lensing effects caused by the bending of light by the cluster mass distribution. In this review we discuss how this phenomenon can be used to determine cluster masses and study the mass distribution itself. As sample sizes increase, the accuracy of the weak Lensing mass estimates needs to improve accordingly. We discuss the main practical aspects of these measurements. We review a number of applications and highlight some recent results.
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weak Gravitational Lensing
arXiv: Astrophysics, 2005Co-Authors: Matthias Bartelmann, M MaturiAbstract:According to the theory of general relativity, masses deflect light in a way similar to convex glass lenses. This Gravitational Lensing effect is astigmatic, giving rise to image distortions. These distortions allow to quantify cosmic structures statistically on a broad range of scales, and to map the spatial distribution of dark and visible matter. We summarise the theory of weak Gravitational Lensing and review applications to galaxies, galaxy clusters and larger-scale structures in the Universe.
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weak Gravitational Lensing
Physics Reports, 2001Co-Authors: Matthias Bartelmann, Peter SchneiderAbstract:Abstract We review theory and applications of weak Gravitational Lensing. After summarising Friedmann–Lemaitre cosmological models, we present the formalism of Gravitational Lensing and light propagation in arbitrary space–times. We discuss how weak-Lensing effects can be measured. The formalism is then applied to reconstructions of galaxy-cluster mass distributions, Gravitational Lensing by large-scale matter distributions, QSO–galaxy correlations induced by weak Lensing, Lensing of galaxies by galaxies, and weak Lensing of the cosmic microwave background.
Ali Ovgun - One of the best experts on this subject based on the ideXlab platform.
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arxiv Gravitational Lensing by rotating wormholes
Physical Review D, 2018Co-Authors: Kimet Jusufi, Ali OvgunAbstract:In this paper the deflection angle of light by a rotating Teo wormhole spacetime is calculated in the weak limit approximation. We mainly focus on the weak deflection angle by revealing the Gravitational Lensing as a partially global topological effect. We apply the Gauss-Bonnet theorem (GBT) to the optical geometry osculating the Teo-Randers wormhole optical geometry to calculate the deflection angle. Furthermore we find the same result using the standard geodesic method. We have found that the deflection angle can be written as a sum of two terms, namely the first term is proportional to the throat of the wormhole and depends entirely on the geometry, while the second term is proportional to the spin angular momentum parameter of the wormhole. A direct observation using Lensing can shed light and potentially test the nature of rotating wormholes by comparing with the black holes systems.
A Barnacka - One of the best experts on this subject based on the ideXlab platform.
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how Gravitational Lensing helps γ ray photons avoid γ γ absorption
The Astrophysical Journal, 2014Co-Authors: A Barnacka, M Bottcher, Iurii SushchAbstract:We investigate potential γ−γ absorption of γ-ray emission from blazars arising from inhomogeneities along the line of sight, beyond the diffuse Extragalactic Background Light (EBL). As plausible sources of excess γ−γ opacity, we consider (1) foreground galaxies, including cases in which this configuration leads to strong Gravitational Lensing, (2) individual stars within these foreground galaxies, and (3) individual stars within our own galaxy, which may act as lenses for microLensing events. We found that intervening galaxies close to the line-of-sight are unlikely to lead to significant excess γ−γ absorption. This opens up the prospect of detecting lensed gamma-ray blazars at energies above 10 GeV with their gamma-ray spectra effectively only affected by the EBL. The most luminous stars located either in intervening galaxy or in our galaxy provides an environment in which these gamma-rays could, in principle, be significantly absorbed. However, despite a large microLensing probability due to stars located in intervening galaxies, γ-rays avoid absorption by being deflected by the Gravitational potentials of such intervening stars to projected distances (“impact parameters”) where the resulting γ − γ opacities are negligible. Thus, neither of the intervening excess photon fields considered here, provide a substantial source of excess γ − γ opacity beyond the EBL, even in the case of very close alignments between the background blazar and a foreground star or galaxy. Subject headings: galaxies: active - galaxies: jets - gamma-rays: Gravitational Lensing - strong, micro
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strong Gravitational Lensing as a tool to investigate the structure of jets at high energies
The Astrophysical Journal, 2014Co-Authors: A Barnacka, Margaret J Geller, Ian P Dellantonio, W BenbowAbstract:The components of blazar jets that emit radiation span a factor of 10 10 in scale. The spatial structure of these emitting regions depends on the observed energy. Photons emitted at different sites cross the lens plane at different distances from the mass-weighted center of the lens. Thus there are differences in magnification ratios and time delays between the images of lensed blazars observed at different energies. When the lens structure and redshift are known from optical observations, these constraints can elucidate the structure of the source at high energies. At these energies, current technology is inadequate to resolve these sources and the observed light curve is thus the sum of the images. Durations of γ-ray flares are short compared with typical time delays; thus both the magnification ratio and the time delay can be measured for the delayed counterparts. These measurements are a basis for localizing the emitting region along the jet. To demonstrate the power of strong Gravitational Lensing, we build a toy model based on the best studied and the nearest relativistic jet M87. Subject headings: Galaxies: active – Gravitational Lensing: strong –gamma-rays: jets
