3,157 research outputs found
Gravitational Radiation from a Naked Singularity. II - Even-Parity Perturbation -
A naked singularity occurs in the generic collapse of an inhomogeneous dust
ball. We study the even-parity mode of gravitational waves from a naked
singularity of the Lema\^{\i}tre-Tolman-Bondi spacetime. The wave equations for
gravitational waves are solved by numerical integration using the single null
coordinate. The result implies that the metric perturbation grows when it
approaches the Cauchy horizon and diverges there, although the naked
singularity is not a strong source of even-parity gravitational radiation.
Therefore, the Cauchy horizon in this spacetime should be unstable with respect
to linear even-parity perturbations.Comment: 16 pages, 5 figures, errors and typos corrected, final versio
Physical Processes in Naked Singularity Formation
Gravitational collapse is one of the most fruitful subjects in gravitational
physics. It is well known that singularity formation is inevitable in complete
gravitational collapse. It was conjectured that such a singularity should be
hidden by horizons if it is formed from generic initial data with physically
reasonable matter fields. Many possible counterexamples to this conjecture have
been proposed over the past three decades, although none of them has proved to
be sufficiently generic. In these examples, there appears a singularity that is
not hidden by horizons. This singularity is called a `naked singularity.' The
appearance of a naked singularity represents the formation of an observable
high-curvature, strong-gravity region. In this paper we review examples of
naked singularity formation and recent progress in research of observable
physical processes - gravitational radiation and quantum particle creation -
from a forming naked singularity.Comment: 76 pages, 25 figure file
On the existence of singularity-free solutions in quartic gravity
We study a general field theory of a scalar field coupled to gravitation
through a quadratic Gauss-Bonnet term . We show that,
under mild assumptions about the function , the classical solutions
in a spatially flat FRW background include singularity - free solutions.Comment: 9 pages, LATEX, uses epsf.tex macro, (1 figure included in
uuencode+compress EPSF form), IOA-29
Confinement and the AdS/CFT Correspondence
We study the thermodynamics of the confined and unconfined phases of
superconformal Yang-Mills in finite volume and at large N using the AdS/CFT
correspondence. We discuss the necessary conditions for a smooth phase
crossover and obtain an N-dependent curve for the phase boundary.Comment: 12 pages, 1 figure, RevTe
Holography and Rotating AdS Black Holes
We probe the AdS/CFT correspondence by comparing the thermodynamics of a
rotating black hole in five-dimensional anti-de Sitter space with that of a
conformal field theory on , whose parameters come from the boundary of
spacetime. In the high temperature limit, we find agreement between gauge
theory and gravity in all thermodynamic quantities upto the same factor of 4/3
that appears for nonrotating holes.Comment: LaTeX, 13 pages, typos corrected, references adde
Red-shifts near black holes
A simple ordinary differential equation is derived governing the red-shifts
of wave-fronts propagating through a non-stationary spherically symmetric
space-time. Approach to an event horizon corresponds to approach to a fixed
point; in general, the phase portrait of the equation illuminates the
qualitative features of the geometry. In particular, the asymptotics of the
red-shift as a horizon is approached, a critical ingredient of Hawking's
prediction of radiation from black holes, are easily brought out. This
asympotic behavior has elements in common with the universal behavior near
phase transitions in statistical physics. The validity of the Unruh vacuum for
the Hawking process can be understood in terms of this universality. The
concept of surface gravity is extended to to non-stationary spherically
symmetric black holes. Finally, it is shown that in the non-stationary case,
Hawking's predicted flux of radiation from a black hole would be modified.Comment: 20 pages, plain Tex, IOP macros, 4 eps figures, accepted by CQ
On the third law of black hole dynamics
The third law of black hole dynamics states that the surface gravity
(temperature) of black hole cannot be reduced to zero in finite sequence of
physical interactions. We argue that the same is true when surface gravity is
replaced by gravitational charge. We demonstrate that the prescribed window for
infalling energy and radiation pinches off as extremality ()
is approached.Comment: 9 pages, LaTeX version, Accepted in Physics Letters
Relationship between Hawking Radiation and Gravitational Anomalies
We show that in order to avoid a breakdown of general covariance at the
quantum level the total flux in each outgoing partial wave of a quantum field
in a black hole background must be equal to that of a (1+1)-dimensional
blackbody at the Hawking temperature.Comment: 5 pages, 1 figure; v2: typo corrected, reference added; v3: comment
added, minor editorial changes to agree with published versio
The Hoop Conjecture in Spherically Symmetric Spacetimes
We give general sufficient conditions for the existence of trapped surfaces
due to concentration of matter in spherically symmetric initial data sets
satisfying the dominant energy condition. These results are novel in that they
apply and are meaningful for arbitrary spacelike slices, that is they do not
require any auxiliary assumptions such as maximality, time-symmetry, or special
extrinsic foliations, and most importantly they can easily be generalized to
the nonspherical case once an existence theory for a modified version of the
Jang equation is developed. Moreover, our methods also yield positivity and
monotonicity properties of the Misner-Sharp energy
Entropy of Rotating Misner String Spacetimes
Using a boundary counterterm prescription motivated by the AdS/CFT
conjecture, I evaluate the energy, entropy and angular momentum of the class of
Kerr-NUT/bolt-AdS spacetimes. As in the non-rotating case, when the NUT charge
is nonzero the entropy is no longer equal to one-quarter of the area due to the
presence of the Misner string. When the cosmological constant is also non-zero,
the entropy is bounded from above.Comment: Revtex, 9 pages, 3 figure
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