41 research outputs found
Energy Conservation and Hawking Radiation
The conservation of energy implies that an isolated radiating black hole
cannot have an emission spectrum that is precisely thermal. Moreover, the
no-hair theorem is only approximately applicable. We consider the implications
for the black hole information puzzle.Comment: 6 pages, LaTex; v2: references adde
The Volume of Black Holes
We propose a definition of volume for stationary spacetimes. The proposed
volume is independent of the choice of stationary time-slicing, and applies
even though the Killing vector may not be globally timelike. Moreover, it is
constant in time, as well as simple: the volume of a spherical black hole in
four dimensions turns out to be just . We then consider
whether it is possible to construct spacetimes that have finite horizon area
but infinite volume, by sending the radius to infinity while making discrete
identifications to preserve the horizon area. We show that, in three or four
dimensions, no such solutions exist that are not inconsistent in some way. We
discuss the implications for the interpretation of the Bekenstein-Hawking
entropy.Comment: 8 pages, revte
De Sitter Space With Finitely Many States: A Toy Story
The finite entropy of de Sitter space suggests that in a theory of quantum
gravity there are only finitely many states. It has been argued that in this
case there is no action of the de Sitter group consistent with unitarity. In
this note we propose a way out of this if we give up the requirement of having
a hermitian Hamiltonian. We argue that some of the generators of the de Sitter
group act in a novel way, namely by mixing in- and out-states. In this way it
is possible to have a unitary S-matrix that is finite-dimensional and,
moreover, de Sitter-invariant. Using Dirac spinors, we construct a simple toy
model that exhibits these features.Comment: 6 pages, LaTe
New Coordinates for de Sitter Space and de Sitter Radiation
We introduce a simple coordinate system covering half of de Sitter space. The
new coordinates have several attractive properties: the time direction is a
Killing vector, the metric is smooth at the horizon, and constant-time slices
are just flat Euclidean space. We demonstrate the usefulness of the coordinates
by calculating the rate at which particles tunnel across the horizon. When
self-gravitation is taken into account, the resulting tunneling rate is only
approximately thermal. The effective temperature decreases through the emission
of radiation.Comment: LaTeX, 10 pages; v2. references added; v3. minor sign errors fixed,
reference added, journal versio
Smooth Initial Conditions from Weak Gravity
CMB measurements reveal an unnaturally smooth early universe. We propose a
mechanism to make this smoothness natural by weakening the strength of gravity
at early times, and therefore altering which initial conditions have low
entropy.Comment: 14 pages, 5 figures. Minor changes, version appearing in PL
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
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