Comment on Ricci Collineations of Static Spherically Symmetric Spacetimes

We present a counter example to a theorem given by Amir {\em et al.} J. Math. Phys. {\bf 35}, 3005 (1994). We also comment on a misleading statements of the same reference.Comment: 4 pages,LaTex fil

On the general structure of Ricci collineations for type B warped spacetimes

A complete study of the structure of Ricci collineations for type B warped spacetimes is carried out. This study can be used as a method to obtain these symetries in such spacetimes. Special cases as 2+2 reducible spacetimes, and plane and spherical symmetric spacetimes are considered specifically.Comment: 18 pages. Version accepted for publication in JM

The Classical Isotropic bi-Dimensional Oscilator in the Eisenhart Formulation of Classical Mechanics

Accordingly with the general theory of relativity, the motion of a particle by the only action of inertia and gravity is described by a space-time geodesic. We use the Eisenhart geometric formulation of classical mechanics to establish a correspondence between geodesics and paths in phase space of the classical bi-dimensional isotropic oscillator. The Killing vectors and its associated constants of motion are presented and compared with nonNoetherian motion constant calculated by S. Hojman and collaborators.   Keywords: Geometric Mechanics, Geometrical and tensorial methods, Formalisms in classical mechanics.De acuerdo con la Teoría de la Relatividad General, el movimiento de partículas por acción de su inercia y la gravedad es descrito por geodésicas en el espacio-tiempo. Utilizamos la formulación Geométrica de Eisenhart de la Mecánica Clásica para establecer una correspondencia entre geodésicas y trayectorias en el espacio de fases del oscilador clásico isótropo. Se presentan los vectores de Killing y las constantes de movimiento asociadas, se comparan con las constantes de movimiento no noetheriano calculadas por S. Hojman y colaboradores

Perturbaciones de carga en objetos compactos

  Se estudia el efecto de las perturbaciones de carga en la estabilidad de objetos compactos, anisótropos relativistas. Se muestra que, al menos para las ecuaciones de estado consideradas, esa estabilidad es muy sensible a fluctuaciones de la carga.      The effect of perturbations of charge on the stability of compact objects is studied. It is shown that, at least for the equations of state considered, the stability of charged matter configurations is very sensible to these fluctuations

Ricci Collineations for Non-Degenerate, Diagonal and Spherically Symmetric Ricci Tensors

The expression of the vector field generator of a Ricci Collineation for diagonal, spherically symmetric and non-degenerate Ricci tensors is obtained. The resulting expressions show that the time and radial first derivatives of the components of the Ricci tensor can be used to classify the collineation, leading to 64 families. Some examples illustrate how to obtain the collineation vector

Vectores de Killing y cantidades conservadas para espacio-tiempos cuasiesféricos

    En este trabajo se estudian los espacio-tiempos con deformación de tipo B, con simetría axial y cuasi-esféricos. Se obtiene un elemento de línea tal que admite vectores de Killing de la familia 1 propuesta por J. Flores et al. [1]. Se encuentran las cantidades conservadas asociadas a estos vectores de Killing y por tanto una primera integral de las ecuaciones de las geodésicas que describen una partícula libre inmersa en este tipo espacio-tiempo.                    The warped space-time type B with axial symmetry and quasi-spherical is explored. This produces a line element that admits killing vector of the family 1-type proposed by J. Flores et al. [1]. The associated conserved amounts with these vectors are found and therefore a first integral of the geodesic equations which describe fres particle inmerse in such space-time is obtained.   &nbsp

Vacuum effects in an asymptotically uniformly accelerated frame with a constant magnetic field

In the present article we solve the Dirac-Pauli and Klein Gordon equations in an asymptotically uniformly accelerated frame when a constant magnetic field is present. We compute, via the Bogoliubov coefficients, the density of scalar and spin 1/2 particles created. We discuss the role played by the magnetic field and the thermal character of the spectrum.Comment: 17 pages. RevTe

Ricci Collineations for type B warped space-times

We present the general structure of proper Ricci Collineations (RC) for type B warped space-times. Within this framework, we give a detailed description of the most general proper RC for spherically symmetric metrics. As examples, static spherically symmetric and Friedmann-Robertson-Walker space-times are considered.Comment: 18 pages, Latex, To appear in GR