Osvaldo M. Moreschi

Intrinsic angular momentum and centre of mass in general relativity

There are several definitions in the literature of the notion of total angular momentum in general relativity. However, none of them can be said to capture the physical notion of intrinsic angular momentum of the sources in the presence of gravitational radiation. We present a definition of angular momentum for radiative spacetimes which does not suffer from any ambiguity of supertranslations. We have succeeded in providing an appropriate notion of intrinsic angular momentum and, at the same time, a definition of centre of mass frame at future null infinity. This notion is required in calculations involving radiation of angular momentum, as, for example, is expected in binary coalescence of black holes.

Rest frame system for asymptotically flat space–times

The notion of center of mass for an isolated system has been previously encoded in the definition of the so-called nice sections. In this article we present a generalization of the proof of existence of solutions to the linearized equation for nice sections, and formalize a local existence proof of nice sections relaxing the radiation condition. We report on the differentiable and non-self-crossing properties of this family of solutions. We also give a proof of the global existence of nice sections.

Study of the Robinson-Trautman metrics in the asymptotic future

A systematic study of the Robinson-Trautman metrics in the asymptotic future is presented. As a by-product another technique, that could be used for determining existence of solutions of the Robinson-Trautman equation, is found. All these metrics present an exponential asymptotic limit to the Schwarzschild metric in this regime.

Photon rockets and the Robinson-Trautman geometries

We point out the relation between the photon rocket spacetimes and the Robinson - Trautman geometries. This allows a discussion of the issues related to the distinction between the gravitational and matter - energy radiation that appear in these metrics in a more geometrical way, taking full advantage of their asymptotic properties at null infinity to separate the Weyl and Ricci radiations, and to clearly establish their gravitational energy content. We also give the exact solution for the generalized photon rockets.

Intrinsic angular momentum for radiating spacetimes which agrees with the Komar integral in the axisymmetric case

Fil: Gallo, Emanuel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Fisica Enrique Gaviola. Universidad Nacional de Cordoba. Instituto de Fisica Enrique Gaviola; Argentina

New derivation for the equations of motion for particles in electromagnetism

We present equations of motion for charged particles using balanced equations, and without introducing explicitly divergent quantities. This derivation contains as particular cases some well known equations of motion, as the Lorentz-Dirac equations. An study of our main equations in terms of order of the interaction with the external field conduces us to the Landau-Lifshitz equations. We find that the analysis in second order show a special behavior. We give an explicit presentation up to third order of our main equations, and expressions for the calculation of general orders.

Peculiar anisotropic stationary spherically symmetric solution of Einstein equations

Motivated by studies on gravitational lenses, we present an exact solution of the field equations of general relativity, which is static and spherically symmetric, has no mass but has a non-vanishing spacelike components of the stress-energy-momentum tensor. In spite of its strange nature, this solution provides with non-trivial descriptions of gravitational effects. We show that the main aspects found in the \emph{dark matter phenomena} can be satisfactorily described by this geometry. We comment on the relevance it could have to consider non-vanishing spacelike components of the stress-energy-momentum tensor ascribed to dark matter.

Approximation Method for the Relaxed Covariant Form of the Gravitational Field Equations for Particles

We present a study of the so called relaxed field equations of general relativity in terms of a decomposition of the metric; which is designed to deal with the notion of particles. Several known results are generalized to a coordinate free covariant discussion. We apply our techniques to the study of a particle up to second order.

Estimating total momentum at finite distances

We study the difficulties associated with the evaluation of the total Bondi momentum at finite distances around the central source of a general (asymptotically flat) spacetime. Since the total momentum is only rigorously defined at future null infinity, both finite distance and gauge effects must be taken into account for a correct computation of this quantity. Our discussion is applicable in general contexts but is particularly relevant in numerically constructed spacetimes for both extracting important physical information and assessing the accuracy of additional quantities.

Estimates of the total gravitational radiation in the head-on black hole collision.

We report on calculations of the total gravitational energy radiated in the head-on black hole collision, where we use the geometry of the Robinson-Trautman metrics.