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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 5005-5022 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Recently there has been developed a reformulation of general relativity (GR)—referred to as the null surface version of GR—where instead of the metric field as the basic variable of the theory, families of three-surfaces in a four-manifold become basic. From these surfaces themselves, a conformal metric, conformal to an Einstein metric, can be constructed. A choice of conformal factor turns it into an Einstein metric. The surfaces are then automatically characteristic surfaces of this metric. In the present paper we explore the linearization of this null surface theory and compare it with the standard linear GR. This allows a better understanding of many of the subtle mathematical issues and sheds light on some of the obscure points of the null surface theory. It furthermore permits a very simple solution generating scheme for the linear theory and the beginning of a perturbation scheme for the full theory. © 1995 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 26 (1985), S. 300-305 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We reexpress the Maxwell field as a cross section of a line bundle over M×S2, the six-dimensional space of null directions on Minkowski space. Maxwell's equations then become a pair of linear equations for a Herz-like scalar on M×S2. We obtain a deeper understanding of the simple, yet nontrivial relationship between the self-dual and the anti-self-dual parts of a real Maxwell field. Our results are then applied to study solutions which are globally regular (on M×S2) namely, the pure radiation solutions, as well as solutions associated with discrete sources (the Lienard–Wiechert fields).
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 37 (1996), S. 3833-3853 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We present a manifestly conformally invariant formulation of Maxwell equations on asymptotically flat space–times. It is shown how to construct regular self-dual and antiself-dual fields from suitable radiation data, and the general solution as a sum of fields with both types of duality. The basic variable in this formalism is a scalar field F defined as the phase of the parallel propagator (associated with the Maxwell potential) from interior points to future null infinity along null geodesics. Field equations equivalent to the source free Maxwell's equations are derived for F. A perturbative solution based on Huygens' principle is proposed. Exact solutions are found for H-spaces. The use of these results on gravitational lensing is discussed. © 1996 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 40 (1999), S. 2483-2493 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: It is shown that the main variable Z of the null surface formulation of GR is the generating family of a constrained Lagrange submanifold that lives on the energy surface H=0 and that its level surfaces Z=const yield Legendre submanifolds on that energy surface. Thus, the singularity structure of past null cones with apex at I+ is obtained by studying the projection map of the Legendre submanifolds to the configuration space. The behavior of the coordinate system defined by the variable Z at the caustic points is analyzed. It is shown that a single function Z(xa,ζ,ζ¯) cannot generate the conformal structure of an asymptotically flat space–time that satisfies the generic and weak energy condition. © 1999 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 38 (1997), S. 4714-4729 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: 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 I. 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. © 1997 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 6397-6416 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We formulate the vacuum Einstein equations as differential equations for two functions, one complex and one real on a six-dimensional manifold, M×S2, with M eventually becoming the space–time and the S2 becoming the sphere of null directions over M. At the start there is no other further structure available: the structure arising from the two functions. The complex function, referred to as Λ[M×S2], encodes information about a sphere's worth of surfaces through each point of M. From knowledge of Λ one can define a second rank tensor on M which can be interpreted as a conformal metric, so that the "surfaces'' are automatically null or characteristics of this conformal metric. The real function, Ω, plays the role of a conformal factor: it converts the conformal metric into a vacuum Einstein metric. Locally, all Einstein metrics can be obtained in this manner. In this work, we fully develop this "null surface version of general relativity (GR):'' we display, discuss and analyze the equations, we show that many of the usual geometric quantities of GR (e.g., the Weyl and Ricci tensors, the optical parameters, etc.) can be easily expressed in terms of the Λ and Ω, we study the gauge freedom and develop a perturbation theory. To conclude, we speculate on the significance and possible classical and quantum uses of this formulation. © 1995 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Foundations of physics 14 (1984), S. 1061-1081 
    ISSN: 1572-9516
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A detailed outline is presented of several convergent points of view connecting the self-dual and anti-self-dual fields with their free data. This is done for the Maxwell and for linearized gravity as exemplifying the approaches. The Sparling equation provides one tool of great power and characterizes one approach. The twistor theory of Penrose yields another equally powerful point of view. The links between these two basic approaches given in this paper provide a unification that allows workers and others with interest in this area to proceed more readily toward the goal of understanding the full nonlinear Einstein equations.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Foundations of physics 15 (1985), S. 487-495 
    ISSN: 1572-9516
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this note we give two new simple derivations of the “good-cut” equation, the equation which governs (complex) self-dual asymptotically flat gravitational fields. One of these derivations is remarkably simple, involving only a few lines. Our main point of interest, however, is in the second derivation. Though it is slightly more complicated, this method of derivation is almost certainly generalizable to cover real asymptotically flat space-times and thus lead to a generalization of the good-cut equation.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    General relativity and gravitation 15 (1983), S. 475-487 
    ISSN: 1572-9532
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract After brief reviews of the Geroch and spin-coefficient formalism approaches to null infinity, we present a dictionary which translates between the two formalisms.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    General relativity and gravitation 17 (1985), S. 343-352 
    ISSN: 1572-9532
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study conformal transformations in four-dimensional manifolds. In particular, we present a new set of two necessary and sufficient conditions for a space to be conformal to an Einstein space. The first condition defines the class of spaces conformal to C spaces, whereas the last one (the vanishing of the Bach tensor) gives the particular subclass ofC spaces which are conformally related to Einstein spaces.
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