4,979 research outputs found
Closed Trapped Surfaces in Cosmology
The existence of closed trapped surfaces need not imply a cosmological
singularity when the spatial hypersurfaces are compact. This is illustrated by
a variety of examples, in particular de Sitter spacetime admits many closed
trapped surfaces and obeys the null convergence condition but is non-singular
in the k=+1 frame.Comment: 11 pages. To appear in GRG, Vol 35 (August issue
Conformal Invariance of Black Hole Temperature
It is shown that the surface gravity and temperature of a stationary black
hole are invariant under conformal transformations of the metric that are the
identity at infinity. More precisely, we find a conformal invariant definition
of the surface gravity of a conformal Killing horizon that agrees with the
usual definition(s) for a true Killing horizon and is proportional to the
temperature as defined by Hawking radiation. This result is reconciled with the
intimate relation between the trace anomaly and the Hawking effect, despite the
{\it non}invariance of the trace anomaly under conformal transformations.Comment: 8 pages, plain LaTeX, NSF-ITP-93-9
The Gravitational Hamiltonian in the Presence of Non-Orthogonal Boundaries
This paper generalizes earlier work on Hamiltonian boundary terms by omitting
the requirement that the spacelike hypersurfaces intersect the
timelike boundary orthogonally. The expressions for the action and
Hamiltonian are calculated and the required subtraction of a background
contribution is discussed. The new features of a Hamiltonian formulation with
non-orthogonal boundaries are then illustrated in two examples.Comment: 23 pages, 1 figure, LaTeX. The action is altered to include a corner
term which results in a different value for the non-orthogonal term. An
additional appendix with Euclidean results is included. To appear in Class.
Quant. Gra
Generalized entropy and Noether charge
We find an expression for the generalized gravitational entropy of Hawking in
terms of Noether charge. As an example, the entropy of the Taub-Bolt spacetime
is calculated.Comment: 6 pages, revtex, reference correcte
Quantum Coherence in Two Dimensions
The formation and evaporation of two dimensional black holes are discussed.
It is shown that if the radiation in minimal scalars has positive energy, there
must be a global event horizon or a naked singularity. The former would imply
loss of quantum coherence while the latter would lead to an even worse
breakdown of predictability. CPT invariance would suggest that there ought to
be past horizons as well. A way in which this could happen with wormholes is
described.Comment: 11 pages, DAMTP-R93/15, CALT-68-1861, Tex, 3 appended uuencoded
figure
A non-singular black hole model as a possible end-product of gravitational collapse
In this paper we present a non-singular black hole model as a possible
end-product of gravitational collapse. The depicted spacetime which is type
[II,(II)], by Petrov classification, is an exact solution of the Einstein
equations and contains two horizons. The equation of state in the radial
direction, is a well-behaved function of the density and smoothly reproduces
vacuum-like behavior near r=0 while tending to a polytrope at larger r, low
density, values. The final equilibrium configuration comprises of a de
Sitter-like inner core surrounded by a family of 2-surfaces of matter fields
with variable equation of state. The fields are all concentrated in the
vicinity of the radial center r=0. The solution depicts a spacetime that is
asymptotically Schwarzschild at large r, while it becomes de Sitter-like for
vanishing r. Possible physical interpretations of the macro-state of the black
hole interior in the model are offered. We find that the possible state admits
two equally viable interpretations, namely either a quintessential intermediary
region or a phase transition in which a two-fluid system is in both dynamic and
thermodynamic equilibrium. We estimate the ratio of pure matter present to the
total energy and in both (interpretations) cases find it to be virtually the
same, being 0.83. Finally, the well-behaved dependence of the density and
pressure on the radial coordinate provides some insight on dealing with the
information loss paradox.Comment: 12 Pages, 1 figure. Accepted for publication in Phys. Rev.
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 fate of black string instabilities: An Observation
Gregory and Laflamme (hep-th/9301052) have argued that an instability causes
the Schwarzschild black string to break up into disjoint black holes. On the
other hand, Horowitz and Maeda (arXiv:hep-th/0105111) derived bounds on the
rate at which the smallest sphere can pinch off, showing that, if it happens at
all, such a pinch-off can occur only at infinite affine parameter along the
horizon. An interesting point is that, if a singularity forms, such an infinite
affine parameter may correspond to a finite advanced time -- which is in fact a
more appropriate notion of time at infinity. We argue below that pinch-off at a
finite advanced time is in fact a natural expectation under the bounds derived
by Horowitz and Maeda.Comment: 4 pages, RevTex, 1 figure, references adde
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
First Order Corrections to the Unruh Effect
First order corrections to the Unruh effect are calculated from a model of an
accelerated particle detector of finite mass. We show that quantum smearing of
the trajectory and large recoil essentially do not modify the Unruh effect.
Nevertheless, we find corrections to the thermal distribution and to the Unruh
temperature. In a certain limit, when the distribution at equilibrium remains
exactly thermal, the corrected temperature is found to be , where is the Unruh temperature. We estimate the consequent
corrections to the Hawking temperature and the black hole entropy, and comment
on the relationship to the problem of trans-planckian frequencies.Comment: 23 pages, LaTe
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