4,149 research outputs found
Quantization in black hole backgrounds
Quantum field theory in a semiclassical background can be derived as an
approximation to quantum gravity from a weak-coupling expansion in the inverse
Planck mass. Such an expansion is studied for evolution on "nice-slices" in the
spacetime describing a black hole of mass M. Arguments for a breakdown of this
expansion are presented, due to significant gravitational coupling between
fluctuations, which is consistent with the statement that existing calculations
of information loss in black holes are not reliable. For a given fluctuation,
the coupling to subsequent fluctuations becomes of order unity by a time of
order M^3. Lack of a systematic derivation of the weakly-coupled/semiclassical
approximation would indicate a role for the non-perturbative dynamics of
gravity, and possibly for the proposal that such dynamics has an essentially
non-local quality.Comment: 28 pages, 4 figures, harvmac. v2: added refs, minor clarification
Relativistic Green functions in a plane wave gravitational background
We consider a massive relativistic particle in the background of a
gravitational plane wave. The corresponding Green functions for both spinless
and spin 1/2 cases, previously computed by A. Barducci and R. Giachetti
\cite{Barducci3}, are reobtained here by alternative methods, as for example,
the Fock-Schwinger proper-time method and the algebraic method. In analogy to
the electromagnetic case, we show that for a gravitational plane wave
background a semiclassical approach is also sufficient to provide the exact
result, though the lagrangian involved is far from being a quadratic one.Comment: Last paper by Professor Arvind Narayan Vaidya, 18 pages, no figure
A Conformal Mapping and Isothermal Perfect Fluid Model
Instead of conformal to flat spacetime, we take the metric conformal to a
spacetime which can be thought of as ``minimally'' curved in the sense that
free particles experience no gravitational force yet it has non-zero curvature.
The base spacetime can be written in the Kerr-Schild form in spherical polar
coordinates. The conformal metric then admits the unique three parameter family
of perfect fluid solution which is static and inhomogeneous. The density and
pressure fall off in the curvature radial coordinates as for
unbounded cosmological model with a barotropic equation of state. This is the
characteristic of isothermal fluid. We thus have an ansatz for isothermal
perfect fluid model. The solution can also represent bounded fluid spheres.Comment: 10 pages, TeX versio
Asymptotically Flat Radiating Solutions in Third Order Lovelock Gravity
In this paper, we present an exact spherically symmetric solution of third
order Lovelock gravity in dimensions which describes the gravitational
collapse of a null dust fluid. This solution is asymptotically (anti-)de Sitter
or flat depending on the choice of the cosmological constant. Using the
asymptotically flat solution for with a power-law form of the mass
as a function of the null coordinate, we present a model for a gravitational
collapse in which a null dust fluid radially injects into an initially flat and
empty region. It is found that a naked singularity is inevitably formed whose
strength is different for the and cases. In the case,
the limiting focusing condition for the strength of curvature singularity is
satisfied. But for , the strength of curvature singularity depends on
the rate of increase of mass of the spacetime. These considerations show that
the third order Lovelock term weakens the strength of the curvature
singularity.Comment: 15 pages, no figure, references added, two appendix adde
A Spherically Symmetric Closed Universe as an Example of a 2D Dilatonic Model
We study the two-dimensional (2D) dilatonic model describing a massless
scalar field minimally coupled to the spherically reduced Einstein-Hilbert
gravity. The general solution of this model is given in the case when a Killing
vector is present. When interpreted in four dimensions, the solution describes
either a static or a homogeneous collision of incoming and outgoing null dust
streams with spherical symmetry. The homogeneous Universe is closed.Comment: 5 pages, 2 figures, to appear in Physical Review
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