Search results for "COSMOLOGY"
showing 10 items of 2905 documents
Simulation-based marginal likelihood for cluster strong lensing cosmology
2015
Comparisons between observed and predicted strong lensing properties of galaxy clusters have been routinely used to claim either tension or consistency with $\Lambda$CDM cosmology. However, standard approaches to such cosmological tests are unable to quantify the preference for one cosmology over another. We advocate approximating the relevant Bayes factor using a marginal likelihood that is based on the following summary statistic: the posterior probability distribution function for the parameters of the scaling relation between Einstein radii and cluster mass, $\alpha$ and $\beta$. We demonstrate, for the first time, a method of estimating the marginal likelihood using the X-ray selected …
An approach to electromagnetism from the general relativity
2010
Classical gravitation is so similar to the electrostatic that the possible unification has been investigated for many years. Although electromagnetism is formulated successfully by quantum field theory, this paper proposes a simple approach to describe the electromagnetism from the macroscopic perspective of general relativity. The hypothesis is based on two charged particles that cause disturbance energy sufficient to disrupt the space-time and explain approximately Maxwell's equations. Therefore, with such this simple idea, we suggest the possibility that the geometric relationship between electromagnetism and gravitation is not yet fully exhausted.
Correcting the effect of stellar spots on ARIEL transmission spectra
2020
The goal of this study is to assess the impact of the stellar spots on the extraction of the planetary transmission spectra observed by ARIEL. We develop a method to model the stellar spectrum of a star in the presence of spots by using the out-of-transit observations. It is based on a chi squared minimization procedure of the out-of-transit spectrum on a grid of stellar spectra with different sizes and temperatures of the spots. The approach allows us also to study the temporal evolution of the spots when comparing stellar spectra observed at different epochs. We also present a method to correct the transit depth variations due to non-occulted stellar spots and estimate the error we introd…
Relativistic Positioning Systems: current status
2009
A {\em relativistic positioning system} consists in a set of four clocks broadcasting their respective proper time by means of light signals. Among them, the more important ones are the {\em auto-located positioning systems,} in which every clock broadcasts not only its proper time but also the proper times that it receives from the other three. At this level, no reference to any exterior system (the Earth surface, for example) and no synchronization are needed. The current status of the theory of relativistic positioning systems is sketched.
Non-linear cosmological collapse of quintessence
2015
We present a study of the fully relativistic spherical collapse in presence of quintessence using on Numerical Relativity, following the method proposed by the authors in a previous article [arXiv:1409.3476]. We ascertain the validity of the method by studying the evolution of a spherically symmetric quintessence inhomogeneity on a de Sitter background and we find that it has an impact on the local expansion around the centre of coordinates. We then proceed to compare the results of our method to those of the more largely adopted top-hat model. We find that quintessence inhomogeneities do build up under the effect that matter inhomogeneities have on the local space-time yet remain very smal…
Denoising of gravitational-wave signal GW150914 via total-variation methods
2016
We apply a regularized Rudin-Osher-Fatemi total variation (TV) method to denoise the transient gravitational wave signal GW150914. We have previously applied TV techniques to denoise numerically generated grav- itational waves embedded in additive Gaussian noise, obtaining satisfactory results irrespective of the signal morphology or astrophysical origin. We find that the non-Gaussian, non-stationary noise from the gravitational wave event GW150914 can also be successfully removed with TV-denoising methods. The quality of the de- noised waveform is comparable to that obtained with the Bayesian approach used in the discovery paper [1]. TV-denoising techniques may thus offer an additional via…
Assessment of a high-resolution central scheme for the solution of the relativistic hydrodynamics equations
2004
We assess the suitability of a recent high-resolution central scheme developed by Kurganov & Tadmor (2000) for the solution of the relativistic hydrodynamics equations. The novelty of this approach relies on the absence of Riemann solvers in the solution procedure. The computations we present are performed in one and two spatial dimensions in Minkowski spacetime. Standard numerical experiments such as shock tubes and the relativistic flat-faced step test are performed. As an astrophysical application the article includes two-dimensional simulations of the propagation of relativistic jets using both Cartesian and cylindrical coordinates. The simulations reported clearly show the capabili…
Depletion in Bose-Einstein condensates using quantum field theory in curved space
2007
5 pages.-- PACS nrs.: 03.75.Kk; 05.30.Jp; 04.62.+v; 04.70.Dy.-- ISI Article Identifier: 000246074600122.-- ArXiv pre-print available at: http://arxiv.org/abs/cond-mat/0610367
Hyperbolic nature of uniformly rotating systems and their relation to gravity
2008
Special relativity corresponds to hyperbolic geometry at constant velocity while the so-called general relativity corresponds to hyperbolic geometry of uniformly accelerated systems. Generalized expressions for angular momentum, centrifugal and Coriolis forces are found in hyperbolic space, which reduce to the usual expressions of Euclidean space when the absolute constant tends to infinity. Gravity enters only in the specification of the absolute constant. A uniformly rotating disc corresponds exactly to hyperbolic geometry with a constant negative Gaussian curvature. The angle defect is related to Lorentz contraction of objects normal to the radial direction. Lobachevsky's angle of parall…
A hydrodynamic approach to the classical ideal gas
2019
The necessary and sufficient condition for a conservative perfect fluid energy tensor to be the energetic evolution of a classical ideal gas is obtained. This condition forces the square of the speed of sound to have the form $c_s^2 = \frac{\gamma p}{\rho+p}$ in terms of the hydrodynamic quantities, energy density $\rho$ and pressure $p$, $\gamma$ being the (constant) adiabatic index. The {\em inverse problem} for this case is also solved, that is, the determination of all the fluids whose evolutions are represented by a conservative energy tensor endowed with the above expression of $c^2_s$, and it shows that these fluids are, and only are, those fulfilling a Poisson law. The relativistic …