Search results for "RELATIVITY"
showing 10 items of 1213 documents
Lens Effect and CMB Anisotropies: Deviations from Gaussianity
2003
The CMB sky can be seen as the superimposition of two components, one of them is the temperature distribution in the absence of lensing and the other one is the correction caused by lensing. In the model under consideration, the first of these components is Gaussian, but the second is not. Numerical methods to calculate angular correlations in the lens component are designed and tested. Some of these correlations are estimated. Deviations from Gaussianity are confirmed.
Geons in Palatini Theories of Gravity
2017
An explicit implementation of geons in the context of gravitational theories extending general relativity is discussed in detail. Such extensions are formulated in the Palatini approach, where metric and affine connection are regarded as independent entities. This formulation is inspired on the macroscopic description of the physics of crystalline structures with defects in the context of solid-state physics, whose study can provide valuable lessons for going beyond GR. We discuss several theories for the gravitational field including additional contributions of the Ricci tensor in four and higher dimensions. As opposed to the standard metric approach, the Palatini formulation generates gho…
Constraints on black-hole charges with the 2017 EHT observations of M87*
2021
Full list of authors: Kocherlakota, Prashant; Rezzolla, Luciano; Falcke, Heino; Fromm, Christian M.; Kramer, Michael; Mizuno, Yosuke; Nathanail, Antonios; Olivares, Héctor; Younsi, Ziri; Akiyama, Kazunori; Alberdi, Antxon; Alef, Walter; Algaba, Juan Carlos; Anantua, Richard; Asada, Keiichi; Azulay, Rebecca; Baczko, Anne-Kathrin; Ball, David; Baloković, Mislav; Barrett, John; Benson, Bradford A.; Bintley, Dan; Blackburn, Lindy; Blundell, Raymond; Boland, Wilfred; Bouman, Katherine L.; Bower, Geoffrey C.; Boyce, Hope; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broderick, Avery E.; Broguiere, Dominique; Bronzwaer, Thomas; Byun, Do-Young; Carlstrom, John E.; …
Cosmic censorship conjecture in some matching spherical collapsing metrics
2017
A physically plausible Lema{\^{\i}}tre-Tolman-Bondi collapse in the marginally bound case is considered. By "physically plausible" we mean that the corresponding metric is ${\cal C}^1$ matched at the collapsing star surface and further that its {\em intrinsic} energy is, as due, stationary and finite. It is proved for this Lema{\^{\i}}tre-Tolman-Bondi collapse, for some parameter values, that its intrinsic central singularity is globally naked, thus violating the cosmic censorship conjecture with, for each direction, one photon, or perhaps a pencil of photons, leaving the singularity and reaching the null infinity. Our result is discussed in relation to some other cases in the current liter…
Stability of the intrinsic energy vanishing in the Schwarzschild metric under a slow rotation
2014
The linearized Kerr metric is considered and put in some Gauss coordinates which are further {\em intrinsic} ones. The linear and angular 4-momenta of this metric are calculated in these coordinates and the resulting value is just zero. Thus, the global vanishing previously found for the Schwarzschild metric remains linearly stable under slow rotational perturbations of this metric.
On the uniqueness of the space-time energy in General Relativity. The illuminating case of the Schwarzschild metric
2013
The case of asymptotic Minkowskian space-times is considered. A special class of asymptotic rectilinear coordinates at the spatial infinity, related to a specific system of free falling observers, is chosen. This choice is applied in particular to the Schwarzschild metric, obtaining a vanishing energy for this space-time. This result is compared with the result of some known theorems on the uniqueness of the energy of any asymptotic Minkowskian space, showing that there is no contradiction between both results, the differences becoming from the use of coordinates with different operational meanings. The suitability of Gauss coordinates when defining an {\em intrinsic} energy is considered a…
R2phase diagram of quantum Einstein gravity and its spectral dimension
2012
Within the gravitational asymptotic safety program, the renormalization group (RG) flow of the ${R}^{2}$ truncation in three and four spacetime dimensions is analyzed in detail. In particular, we construct RG trajectories which emanate from the non-Gaussian UV fixed point and possess long classical regimes where the effective average action is well approximated by the classical Einstein-Hilbert action. As an application we study the spectral dimension of the effective quantum Einstein gravity spacetimes resulting from these trajectories, establishing that the picture of a multifractal spacetime is robust under the extension of the truncated theory space. We demonstrate that regimes of const…
Revisiting the quantum scalar field in spherically symmetric quantum gravity
2012
We extend previous results in spherically symmetric gravitational systems coupled with a massless scalar field within the loop quantum gravity framework. As starting point, we take the Schwarzschild spacetime. The results presented here rely on the uniform discretization method. We are able to minimize the associated discrete master constraint using a variational method. The trial state for the vacuum consists of a direct product of a Fock vacuum for the matter part and a Gaussian centered around the classical Schwarzschild solution. This paper follows the line of research presented by Gambini, Pullin and Rastgoo and a comparison between their result and the one given in this work is made.
Focus on modern frontiers of matter wave optics and interferometry
2012
The level of experimental control and the detailed theoretical understanding of matter wave physics have led to a renaissance of experiments testing the very foundations of quantum mechanics and general relativity, as well as to applications in metrology. A variety of interferometric quantum sensors surpasses, or will surpass, the limits of their classical counterparts, for instance in the measurement of frequency and time or forces such as accelerations due to rotation and gravity with applications in basic science, navigation and the search for natural resources. The collection of original articles published in this focus issue of New Journal of Physics is intended as a snapshot of the cu…
Cosmological solutions in theD=5 Einstein-Maxwell theory coupled to matter
1991
We study the Einstein-Maxwell theory in five dimensions coupled to matter in two distinct ways. In the first we reduce the Lagrangian to an effective four-dimension one and then we couple it to matter; in the second, we introduce matter directly in the original five-dimensional theory. In both cases we use a non trivial configuration for the Maxwell potential. We find non singular solutions which present a repulsive gravitational phase. When this phase is absent, the initial singularity is unavoidable.