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Search Results: 1 - 10 of 51307 matches for " Carlos Kozameh "
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Light Propagation on Quantum Curved Spacetime and Back reaction effects
Carlos Kozameh,Florencia Parisi
Physics , 2007, DOI: 10.1088/0264-9381/24/17/013
Abstract: We study the electromagnetic field equations on an arbitrary quantum curved background in the semiclassical approximation of Loop Quantum Gravity. The effective interaction hamiltonian for the Maxwell and gravitational fields is obtained and the corresponding field equations, which can be expressed as a modified wave equation for the Maxwell potential, are derived. We use these results to analyze electromagnetic wave propagation on a quantum Robertson-Walker space time and show that Lorentz Invariance is not preserved. The formalism developed can be applied to the case where back reaction effects on the metric due to the electromagnetic field are taken into account, leading to non covariant field equations.
Spin and Center of Mass in Axially Symmetric Einstein-Maxwell Spacetimes
Carlos N. Kozameh,Gonzalo Quiroga
Physics , 2012, DOI: 10.1088/0264-9381/29/23/235006
Abstract: We give a definition and derive the equations of motion for the center of mass and angular momentum of an axially symmetric, isolated system that emits gravitational and electromagnetic radiation. A central feature of this formulation is the use of Newman-Unti cuts at null infinity that are generated by worldlines of the spacetime. We analyze some consequences of the results and comment on the generalization of this work to general asymptotically flat spacetimes.
Asymptotically Shear-free and Twist-free Null Geodesic Congruences
Carlos Kozameh,Ezra T. Newman
Physics , 2007, DOI: 10.1088/0264-9381/24/11/019
Abstract: We show that, though they are rare, there are asymptotically flat space-times that possess null geodesic congruences that are both asymptotically shear- free and twist-free (surface forming). In particular, we display the class of space-times that possess this property and demonstrate how these congruences can be found. A special case within this class are the Robinson- Trautman space-times. In addition, we show that in each case the congruence is isolated in the sense that there are no other neighboring congruences with this dual property.
GR via Characteristic Surfaces
Simonetta Frittelli,Carlos Kozameh,Ted Newman
Physics , 1995, DOI: 10.1063/1.531210
Abstract: We reformulate the Einstein equations as equations for families of surfaces on a four-manifold. These surfaces eventually become characteristic surfaces for an Einstein metric (with or without sources). In particular they are formulated in terms of two functions on R4xS2, i.e. the sphere bundle over space-time, - one of the functions playing the role of a conformal factor for a family of associated conformal metrics, the other function describing an S2's worth of surfaces at each space-time point. It is from these families of surfaces themselves that the conformal metric - conformal to an Einstein metric - is constructed; the conformal factor turns them into Einstein metrics. The surfaces are null surfaces with respect to this metric.
Lorentzian Metrics from Characteristic Surfaces
Simonetta Frittelli,Carlos Kozameh,Ted Newman
Physics , 1995, DOI: 10.1063/1.531209
Abstract: The following issue is raised and discussed; when do families of foliations by hypersurfaces on a given four dimensional manifold become the null surfaces of some unknown, but to be determined, metric $g_{ab}(x)$? It follows from these results that one can use these surfaces as fundamental variables for GR.
Conformal Einstein equations and Cartan conformal connection
Carlos Kozameh,Ezra T Newman,Pawel Nurowski
Physics , 2003, DOI: 10.1088/0264-9381/20/14/305
Abstract: Necessary and sufficient conditions for a space-time to be conformal to an Einstein space-time are interpreted in terms of curvature restrictions for the corresponding Cartan conformal connection.
The Large Footprints of H-Space on Asymptotically Flat Space-Times
Carlos N. Kozameh,Ezra T. Newman
Physics , 2005, DOI: 10.1088/0264-9381/22/22/001
Abstract: We show that certain structures defined on the complex four dimensional space known as H-Space have considerable relevance for its closely associated asymptotically flat real physical space-time. More specifically for every complex analytic curve on the H-space there is an asymptotically shear-free null geodesic congruence in the physical space-time. There are specific geometric structures that allow this world-line to be chosen in a unique canonical fashion giving it physical meaning and significance.
Electromagnetic Dipole Radiation Fields, Shear-Free Congruences and Complex Center of Charge World Lines
Carlos N. Kozameh,Ezra T. Newman
Physics , 2005, DOI: 10.1088/0264-9381/22/22/002
Abstract: We show that for asymptotically vanishing Maxwell fields in Minkowski space with non-vanishing total charge, one can find a unique geometric structure, a null direction field, at null infinity. From this structure a unique complex analytic world-line in complex Minkowski space that can be found and then identified as the complex center of charge. By ''sitting'' - in an imaginary sense, on this world-line both the (intrinsic) electric and magnetic dipole moments vanish. The (intrinsic) magnetic dipole moment is (in some sense) obtained from the `distance' the complex the world line is from the real space (times the charge). This point of view unifies the asymptotic treatment of the dipole moments For electromagnetic fields with vanishing magnetic dipole moments the world line is real and defines the real (ordinary center of charge). We illustrate these ideas with the Lienard-Wiechert Maxwell field. In the conclusion we discuss its generalization to general relativity where the complex center of charge world-line has its analogue in a complex center of mass allowing a definition of the spin and orbital angular momentum - the analogues of the magnetic and electric dipole moments.
Cartan's equivalence method and null coframes in General Relativity
Emanuel Gallo,Mirta Iriondo,Carlos Kozameh
Physics , 2004, DOI: 10.1088/0264-9381/22/9/025
Abstract: Using Cartan's equivalence method for point transformations we obtain from first principles the conformal geometry associated with third order ODEs and a special class of PDEs in two dimensions. We explicitly construct the null tetrads of a family of Lorentzian metrics, the conformal group in three and four dimensions and the so called normal metric connection. A special feature of this connection is that the non vanishing components of its torsion depend on one relative invariant, the (generalized) W\"unschmann Invariant. We show that the above mentioned construction naturally contains the Null Surface Formulation of General Relativity.
Null Surfaces and the Bach Equations
Mirta Iriondo,Carlos N. Kozameh,Alejandra Rojas
Physics , 1999, DOI: 10.1063/1.532117
Abstract: It is shown that the integrability conditions that arise in the Null Surface Formulation (NSF) of general relativity (GR) impose a field equation on the local null surfaces which is equivalent to the vanishing of the Bach tensor. This field equation is written explicitly to second order in a perturbation expansion. The field equation is further simplified if asymptotic flatness is imposed on the underlying space-time. The resulting equation determines the global null surfaces of asymptotically flat, radiative space-times. It is also shown that the source term of this equation is constructed from the free Bondi data at future null infinity. Possible generalizations of this field equation are analyzed. In particular we include other field equations for surfaces that have already appeared in the literature which coincide with ours at a linear level. We find that the other equations do not yield null surfaces for GR.
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