Search results for "Relativity"
showing 10 items of 1213 documents
Accretion-induced quasinormal mode excitation of a Schwarzschild black hole
2007
By combining the numerical solution of the nonlinear hydrodynamics equations with the solution of the linear inhomogeneous Zerilli-Moncrief and Regge-Wheeler equations we investigate the properties of the gravitational radiation emitted during the axisymmetric accretion of matter onto a Schwarzschild black hole. The matter models considered include quadrupolar dust shells and thick accretion disks, permitting us to simulate situations which may be encountered at the end stages of stellar gravitational collapse or binary neutron star merger. We focus on the interference pattern appearing in the energy spectra of the emitted gravitational waves and on the amount of excitation of the quasi-nor…
Dynamical Aspects of Generalized Palatini Theories of Gravity
2009
We study the field equations of modified theories of gravity in which the Lagrangian is a general function of the Ricci scalar and Ricci-squared terms in Palatini formalism. We show that the independent connection can be expressed as the Levi-Civitagrave connection of an auxiliary metric which, in particular cases of interest, is related with the physical metric by means of a disformal transformation. This relation between physical and auxiliary metric boils down to a conformal transformation in the case of f(R) theories. We also show with explicit models that the inclusion of Ricci-squared terms in the action can impose upper bounds on the accessible values of pressure and density, which m…
Canonical equivalence of a generic 2-D dilaton gravity model and a free field
1997
We show that a canonical transformation converts, up to a boundary term, a generic 2-D dilaton gravity model into a free field theory with a Minkowskian target space.
A Quantum Mechanical Model of the Reissner-Nordstrom Black Hole
1997
We consider a Hamiltonian quantum theory of spherically symmetric, asymptotically flat electrovacuum spacetimes. The physical phase space of such spacetimes is spanned by the mass and the charge parameters $M$ and $Q$ of the Reissner-Nordstr\"{o}m black hole, together with the corresponding canonical momenta. In this four-dimensional phase space, we perform a canonical transformation such that the resulting configuration variables describe the dynamical properties of Reissner-Nordstr\"{o}m black holes in a natural manner. The classical Hamiltonian written in terms of these variables and their conjugate momenta is replaced by the corresponding self-adjoint Hamiltonian operator, and an eigenv…
Toward a New Test of the Relativistic Time Dilation Factor by Laser Spectroscopy of Fast Ions in a Storage Ring
2003
The frequency measurement of Doppler-shifted optical lines of ions circulating in a storage ring at high speed permits a sensitive test of the relativistic Doppler-formula and, hence, the time dilation factor γSR of special relativity. Previous measurements at the storage ring TSR with 7Li+ at v = 0.065c gave a new, improved limit, but were hampered by the large observed linewidth, exceeding the natural width 15-fold. Recently we have identified the broadening to be caused by velocity-changing processes in the storage ring. Saturation spectroscopy has proven to be largely immune against these effects and has yielded linewidths only a few MHz larger than the natural one. This is the major in…
Combinatorics of theSU(2)black hole entropy in loop quantum gravity
2009
We use the combinatorial and number-theoretical methods developed in previous works by the authors to study black hole entropy in the new proposal put forth by Engle, Noui, and Perez. Specifically, we give the generating functions relevant for the computation of the entropy and use them to derive its asymptotic behavior, including the value of the Immirzi parameter and the coefficient of the logarithmic correction.
Mathematical Issues in a Fully-Constrained Formulation of Einstein Equations
2008
Bonazzola, Gourgoulhon, Grandcl\'ement, and Novak [Phys. Rev. D {\bf 70}, 104007 (2004)] proposed a new formulation for 3+1 numerical relativity. Einstein equations result, according to that formalism, in a coupled elliptic-hyperbolic system. We have carried out a preliminary analysis of the mathematical structure of that system, in particular focusing on the equations governing the evolution for the deviation of a conformal metric from a flat fiducial one. The choice of a Dirac's gauge for the spatial coordinates guarantees the mathematical characterization of that system as a (strongly) hyperbolic system of conservation laws. In the presence of boundaries, this characterization also depen…
Phenomenological approaches of inflation and their equivalence
2014
In this work, we analyze two possible alternative and model-independent approaches to describe the inflationary period. The first one assumes a general equation of state during inflation due to Mukhanov, while the second one is based on the slow-roll hierarchy suggested by Hoffman and Turner. We find that, remarkably, the two approaches are equivalent from the observational viewpoint, as they single out the same areas in the parameter space, and agree with the inflationary attractors where successful inflation occurs. Rephrased in terms of the familiar picture of a slowly rolling, canonically normalized scalar field, the resulting inflaton excursions in these two approaches are almost ident…
A new stochastic approach to cumulative weak lensing
2009
We study the weak gravitational lensing effects caused by a stochastic distribution of dark matter halos. We develop a simple approach to calculate the magnification probability distribution function which allows us to easily compute the magnitude bias and dispersion for an arbitrary data sample and a given universe model. As an application we consider the effects of single-mass large-scale cosmic inhomogeneities to the SNe magnitude-redshift relation, and conclude that such structures could bias the PDF enough to affect the extraction of cosmological parameters from the limited size of present-day SNe data samples. We also release turboGL, a simple and very fast (<= 1s) Mathematica code…
Intrinsic energy of Lema\^itre-Tolman-Bondi models and cosmological implications
2013
Recently, some Lema{\^{\i}}tre-Tolman-Bondi metrics have been considered as models alternative to the dark energy within the Friedmann-Lema{\^{\i}}tre-Robertson-Walker universes. The vanishing of the intrinsic energy of these metrics is examined since such a vanishing, in the present case and in general, could be interpreted as a necessary condition to consider the possibility of the quantum creation of a metric. More specifically, this vanishing is examined in the particular case where the Lema{\^{\i}}tre-Tolman-Bondi metrics behave asymptotically like a Friedmann-Lema{\^{\i}}tre-Robertson-Walker universe. Finally, we deal with a particular model ruled out after being confronted with cosmi…