30 research outputs found
Trap Target Studies
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
CE-30 - Toward a Trapped Particle Target
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
Trapped surfaces in prolate collapse in the Gibbons-Penrose construction
We investigate existence and properties of trapped surfaces in two models of
collapsing null dust shells within the Gibbons-Penrose construction. In the
first model, the shell is initially a prolate spheroid, and the resulting
singularity forms at the ends first (relative to a natural time slicing by flat
hyperplanes), in analogy with behavior found in certain prolate collapse
examples considered by Shapiro and Teukolsky. We give an explicit example in
which trapped surfaces are present on the shell, but none exist prior to the
last flat slice, thereby explicitly showing that the absence of trapped
surfaces on a particular, natural slicing does not imply an absence of trapped
surfaces in the spacetime. We then examine a model considered by Barrabes,
Israel and Letelier (BIL) of a cylindrical shell of mass M and length L, with
hemispherical endcaps of mass m. We obtain a "phase diagram" for the presence
of trapped surfaces on the shell with respect to essential parameters and . It is found that no trapped surfaces are
present on the shell when or are sufficiently small. (We are
able only to search for trapped surfaces lying on the shell itself.) In the
limit , the existence or nonexistence of trapped surfaces lying
within the shell is seen to be in remarkably good accord with the hoop
conjecture.Comment: 22 pages, 6 figure
No-horizon theorem for vacuum gravity with spacelike G1 isometry groups
We show that (3+1) vacuum spacetimes admitting a global, spacelike,
one-parameter Lie group of isometries of translational type cannot contain
apparent horizons. The only assumption made is that of the existence of a
global spacelike Killing vector field with infinite open orbits; the
four-dimensional vacuum spacetime metric is otherwise arbitrary. This result
may thus be viewed as a hoop conjecture theorem for vacuum gravity with one
spacelike translational Killing symmetry.Comment: 6 pages, revtex4; published in Phys. Rev. D Rapid Com
No-horizon theorem for spacetimes with spacelike G1 isometry groups
We consider four-dimensional spacetimes which obey the
Einstein equations , and admit a global spacelike
isometry group. By means of dimensional reduction and local
analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on
which guarantees that cannot contain apparent
horizons. Given any (3+1) spacetime with spacelike translational isometry, the
no-horizon condition can be readily tested without the need for dimensional
reduction. This provides thus a useful and encompassing apparent horizon test
for -symmetric spacetimes. We argue that this adds further evidence
towards the validity of the hoop conjecture, and signals possible violations of
strong cosmic censorship.Comment: 8 pages, LaTeX, uses IOP package; published in Class. Quantum Gra
Does the generalized second law require entropy bounds for a charged system?
We calculate the net change in generalized entropy occurring when one carries
out the gedanken experiment in which a box initially containing energy ,
entropy and charge is lowered adiabatically toward a
Reissner-Nordstr\"{o}m black hole and then dropped in. This is an extension of
the work of Unruh-Wald to a charged system (the contents of the box possesses a
charge ). Their previous analysis showed that the effects of acceleration
radiation prevent violation of the generalized second law of thermodynamics. In
our more generic case, we show that the properties of the thermal atmosphere
are equally important when charge is present. Indeed, we prove here that an
equilibrium condition for the the thermal atmosphere and the physical
properties of ordinary matter are sufficient to enforce the generalized second
law. Thus, no additional assumptions concerning entropy bounds on the contents
of the box need to be made in this process. The relation between our work and
the recent works of Bekenstein and Mayo, and Hod (entropy bound for a charged
system) are also discussed.Comment: 18pages, RevTex, no figure
Moving black holes via singularity excision
We present a singularity excision algorithm appropriate for numerical
simulations of black holes moving throughout the computational domain. The
method is an extension of the excision procedure previously used to obtain
stable simulations of single, non-moving black holes. The excision procedure
also shares elements used in recent work to study the dynamics of a scalarfield
in the background of a single, boosted black hole. The robustness of our
excision method is tested with single black-hole evolutions using a coordinate
system in which the coordinate location of the black hole, and thus the
excision boundary, moves throughout the computational domain.Comment: 9 pages and 11 figure
Non-Archimedean character of quantum buoyancy and the generalized second law of thermodynamics
Quantum buoyancy has been proposed as the mechanism protecting the
generalized second law when an entropy--bearing object is slowly lowered
towards a black hole and then dropped in. We point out that the original
derivation of the buoyant force from a fluid picture of the acceleration
radiation is invalid unless the object is almost at the horizon, because
otherwise typical wavelengths in the radiation are larger than the object. The
buoyant force is here calculated from the diffractive scattering of waves off
the object, and found to be weaker than in the original theory. As a
consequence, the argument justifying the generalized second law from buoyancy
cannot be completed unless the optimal drop point is next to the horizon. The
universal bound on entropy is always a sufficient condition for operation of
the generalized second law, and can be derived from that law when the optimal
drop point is close to the horizon. We also compute the quantum buoyancy of an
elementary charged particle; it turns out to be negligible for energetic
considerations. Finally, we speculate on the significance of the absence from
the bound of any mention of the number of particle species in nature.Comment: RevTeX, 16 page
A Reformulation of the Hoop Conjecture
A reformulation of the Hoop Conjecture based on the concept of trapped circle
is presented. The problems of severe compactness in every spatial direction,
and of how to superpose the hoops with the surface of the black hole, are
resolved. A new conjecture concerning "peeling" properties of
dynamical/trapping horizons is propounded. A novel geometric Hoop inequality is
put forward. The possibility of carrying over the results to arbitrary
dimension is discussed.Comment: 6 pages, no figures. New references included, typos corrected,
explanatory comments added. Much shorter version, in order to match EPL
length restrictions. To be published in EP