118927729
Stability properties of black holes in self-gravitating nonlinear electrodynamics
We analyze the dynamical stability of black hole solutions in self-gravitating nonlinear electrodynamics with respect to arbitrary linear fluctuations of the metric and electromagnetic field. In particular, we derive simple conditions on the electromagnetic Lagrangian which imply linear stability in the domain of outer communication. We show that these conditions hold for several of the regular black hole solutions found by Ay\'on-Beato and Garc\'{\i}a.
9440626
Plasma focus based repetitive source of fusion neutrons and hard x-rays
A plasma focus device capable of operating at 0.2 pulses per second during several minutes is used as a source of hard x-rays and fast neutrons. An experimental demonstration of the use of the neutrons emissions for radiation probing of hydrogenated substances is presented, showing a particular application in detecting water concentrations differences in the proximity of the device by elastic scattering. Moreover, the device produces ultrashort hard x-rays pulses useful for introspective images of small objects, static or in fast motion, suitable for the identification of internal submillimetric defects. Clear images of metallic objects shielded by several millimeters iron walls are shown.PACS Codes: 29.25.Dz,52.59.Px
15903445
GRAVITATIONAL PERTURBATIONS OF THE KERR BLACK HOLE DUE TO ARBITRARY SOURCES
We describe the Kerr black hole in the ingoing and outgoing Kerr–Schild horizon penetrating coordinates. Starting from the null vector naturally defined in these coordinates, we construct the null tetrad for each case, as well as the corresponding geometrical quantities allowing us to explicitly derive the field equations for the perturbed scalar projections Ψ0(1) and Ψ4(1) of the Weyl tensor, including arbitrary source terms. This perturbative description, including arbitrary sources, described in horizon penetrating coordinates is desirable in several lines of research on black holes, and contributes to the implementation of a formalism aimed to study the evolution of the spacetime in the region where two black holes are close together.
119252183
Gravitational waves during inflation from a 5D large-scale repulsive gravity model
Abstract We investigate, in the transverse traceless (TT) gauge, the generation of the relic background of gravitational waves, generated during the early inflationary stage, on the framework of a large-scale repulsive gravity model. We calculate the spectrum of the tensor metric fluctuations of an effective 4D Schwarzschild–de Sitter metric on cosmological scales. This metric is obtained after implementing a planar coordinate transformation on a 5D Ricci-flat metric solution, in the context of a non-compact Kaluza–Klein theory of gravity. We found that the spectrum is nearly scale invariant under certain conditions. One interesting aspect of this model is that it is possible to derive the dynamical field equations for the tensor metric fluctuations, valid not just at cosmological scales, but also at astrophysical scales, from the same theoretical model. The astrophysical and cosmological scales are determined by the gravity–antigravity radius, which is a natural length scale of the model, that indicates when gravity becomes repulsive in nature.
119111308
Gravitational waves from scalar field accretion
Our aim in this work is to outline some physical consequences of the interaction between black holes and scalar field halos in terms of gravitational waves. In doing so, the black hole is taken as a static and spherically symmetric gravitational source, {\it i. e.} the Schwarzschild black hole, and we work within the test field approximation, considering that the scalar field lives in the curved space-time outside the black hole. We focused on the emission of gravitational waves when the black hole is perturbed by the surrounding scalar field matter. The symmetries of the spacetime and the simplicity of the matter source allow, by means of a spherical harmonic decomposition, to study the problem by means of a one dimensional description. Some properties of such gravitational waves are discussed as a function of the parameters of the infalling scalar field, and allow us to make the conjecture that the gravitational waves carry information on the type of matter that generated them.
120918300
On gravitational waves generated during inflation under the influence of a dynamical cosmological “constant”
We study cosmological gravitational waves generated during inflation under the influence of a decaying cosmological “constant”, in the Transverse-Traceless (TT) gauge. In our approach we consider a non-perturbative contribution of the dynamical cosmological “constant” to the tensor modes. As an application of the model we study the well-known cases $ \Lambda(t)=\sigma H^2$ and $ \Lambda(t)=\vartheta H$ . The spectrum of gravitational waves for the first case results scale invariant at the end of inflation, whereas for the second case scale invariance is not achieved, leaving this to new proposals of the form: $ \Lambda(t)=f(H,H^{2})$ , in order to include inflation in some $ \Lambda(t)CDM$ models. We also found that the non-perturbative contributions of $ \Lambda$(t) , accelerate the decreasing of the amplitude of gravitational waves during a power law inflationary stage, by an exponential factor.
121404671
Spaces of positive and negative frequency solutions of field equations in curved space–times. I. The Klein–Gordon equation in stationary space–times
In stationary space–times Vn×R with compact space‐section manifold without boundary Vn, the Klein–Gordon equation is solved by the one‐parameter group of unitary operators generated by the energy operator i−1T−1 in the Sobolev spaces Hl(Vn) ×Hl−1(Vn). The canonical symplectic and complex structures of the associated dynamical system are calculated. The existence and the uniqueness of the Lichnerowicz kernel are established. The Hilbert spaces of positive and negative frequency‐part solutions defined by means of this kernel are constructed.
121207295
Spaces of positive and negative frequency solutions of field equations in curved space–times. II. The massive vector field equations in static space–times
The space–times considered in this article are static, Vn×R, with compact space‐section manifolds without boundary, Vn, and such that the trajectories of the Killing vector field are geodesics. For the physical field of spin 1 and mass m≳0 in these space–times, field equations are solved in any adapted atlas, by the one‐parameter groups of unitary operators generated by scalar and vector Hamiltonians, i−1Tj−1, j=0,1, in Sobolev spaces Hjl−1(Vn) ×Hjl 1(Vn), leR. Hilbert spaces of positive energy solutions of field equations, as well as those of reduced solutions and their canonical symplectic and complex structures, are determined. The existence and the uniqueness of Lichnerowicz’s (1−1) current on space–time are established, and the corresponding frequency‐solution Hilbert spaces are constructed. Within the framework of Segal, a definition of quantum field operators is given, leading to the postulated commutator for the physical field concerned.