460 research outputs found
Bound states and the Bekenstein bound
We explore the validity of the generalized Bekenstein bound, S <= pi M a. We
define the entropy S as the logarithm of the number of states which have energy
eigenvalue below M and are localized to a flat space region of width a. If
boundary conditions that localize field modes are imposed by fiat, then the
bound encounters well-known difficulties with negative Casimir energy and large
species number, as well as novel problems arising only in the generalized form.
In realistic systems, however, finite-size effects contribute additional
energy. We study two different models for estimating such contributions. Our
analysis suggests that the bound is both valid and nontrivial if interactions
are properly included, so that the entropy S counts the bound states of
interacting fields.Comment: 35 page
Fluctuations of an evaporating black hole from back reaction of its Hawking radiation: Questioning a premise in earlier work
This paper delineates the first steps in a systematic quantitative study of
the spacetime fluctuations induced by quantum fields in an evaporating black
hole. We explain how the stochastic gravity formalism can be a useful tool for
that purpose within a low-energy effective field theory approach to quantum
gravity. As an explicit example we apply it to the study of the
spherically-symmetric sector of metric perturbations around an evaporating
black hole background geometry. For macroscopic black holes we find that those
fluctuations grow and eventually become important when considering sufficiently
long periods of time (of the order of the evaporation time), but well before
the Planckian regime is reached. In addition, the assumption of a simple
correlation between the fluctuations of the energy flux crossing the horizon
and far from it, which was made in earlier work on spherically-symmetric
induced fluctuations, is carefully analyzed and found to be invalid. Our
analysis suggests the existence of an infinite amplitude for the fluctuations
of the horizon as a three-dimensional hypersurface. We emphasize the need for
understanding and designing operational ways of probing quantum metric
fluctuations near the horizon and extracting physically meaningful information.Comment: 10 pages, REVTeX; minor changes, a few references added and a brief
discussion of their relevance included. To appear in the proceedings of the
10th Peyresq meeting. Dedicated to Rafael Sorkin on the occasion of his 60th
birthda
Ten Proofs of the Generalized Second Law
Ten attempts to prove the Generalized Second Law of Thermodyanmics (GSL) are
described and critiqued. Each proof provides valuable insights which should be
useful for constructing future, more complete proofs. Rather than merely
summarizing previous research, this review offers new perspectives, and
strategies for overcoming limitations of the existing proofs. A long
introductory section addresses some choices that must be made in any
formulation the GSL: Should one use the Gibbs or the Boltzmann entropy? Should
one use the global or the apparent horizon? Is it necessary to assume any
entropy bounds? If the area has quantum fluctuations, should the GSL apply to
the average area? The definition and implications of the classical,
hydrodynamic, semiclassical and full quantum gravity regimes are also
discussed. A lack of agreement regarding how to define the "quasi-stationary"
regime is addressed by distinguishing it from the "quasi-steady" regime.Comment: 60 pages, 2 figures, 1 table. v2: corrected typos and added a
footnote to match the published versio
Thermodynamics Inducing Massive Particles' Tunneling and Cosmic Censorship
By calculating the change of entropy, we prove that the first law of black
hole thermodynamics leads to the tunneling probability of massive particles
through the horizon, including the tunneling probability of massive charged
particles from the Reissner-Nordstr\"om black hole and the Kerr-Newman black
hole. Novelly, we find the trajectories of massive particles are close to that
of massless particles near the horizon, although the trajectories of massive
charged particles may be affected by electromagnetic forces. We show that
Hawking radiation as massive particles tunneling does not lead to violation of
the weak cosmic-censorship conjecture
Averaged Energy Conditions and Evaporating Black Holes
In this paper the averaged weak (AWEC) and averaged null (ANEC) energy
conditions, together with uncertainty principle-type restrictions on negative
energy (``quantum inequalities''), are examined in the context of evaporating
black hole backgrounds in both two and four dimensions. In particular,
integrals over only half-geodesics are studied. We determine the regions of the
spacetime in which the averaged energy conditions are violated. In all cases
where these conditions fail, there appear to be quantum inequalities which
bound the magnitude and extent of the negative energy, and hence the degree of
the violation. The possible relevance of these results for the validity of
singularity theorems in evaporating black hole spacetimes is discussed.Comment: Sections 2.1 and 2.2 have been revised and some erroneous statements
corrected. The main conclusions and the figures are unchanged. 27 pp, plain
Latex, 3 figures available upon reques
Prevalence of dental disorders in an abattoir population of horses in South Africa by oral examination of intact and bisected heads
Dental care is an integral part of equine veterinary practice. The objectives of
this cross sectional study were to describe the prevalence of dental disorders in an
abattoir population of horses, and to compare oral examination of intact and bisected
heads. Heads from 40 horses were examined, 19 males and 21 females, divided into
immature, adults and older horses. Older horses in this abattoir population had a
significantly higher prevalence of infundibular caries (91.7%), diastemata (66.7%)
and fractures (58.3%), whereas dental wear disorders affected all age groups.
Gasterophilus larvae were detected in 20% of the horses. The oral examination
performed on intact heads was adequate for diagnosing gross disorders, but further
examination is needed for reliably diagnosing minor disorders.Abe Bailey Trust, the Department of Companion Animal Clinical Studies, Faculty of Veterinary Science Research Fund, and the South African Veterinary Foundation.http://www.elsevier.com/locate/tvjlhb2016Companion Animal Clinical StudiesProduction Animal Studie
Closed Timelike Curves and Holography in Compact Plane Waves
We discuss plane wave backgrounds of string theory and their relation to
Goedel-like universes. This involves a twisted compactification along the
direction of propagation of the wave, which induces closed timelike curves. We
show, however, that no such curves are geodesic. The particle geodesics and the
preferred holographic screens we find are qualitatively different from those in
the Goedel-like universes. Of the two types of preferred screen, only one is
suited to dimensional reduction and/or T-duality, and this provides a
``holographic protection'' of chronology. The other type of screen, relevant to
an observer localized in all directions, is constructed both for the compact
and non-compact plane waves, a result of possible independent interest. We
comment on the consistency of field theory in such spaces, in which there are
closed timelike (and null) curves but no closed timelike (or null) geodesics.Comment: 21 pages, 3 figures, LaTe
Scaling of the B and D meson spectrum in lattice QCD
We give results for the and the meson spectrum using NRQCD on the
lattice in the quenched approximation. The masses of radially and orbitally
excited states are calculated as well as -wave hyperfine and -wave fine
structure. Radially excited -states are observed for the first time. Radial
and orbital excitation energies match well to experiment, as does the
strange-non-strange -wave splitting. We compare the light and heavy quark
mass dependence of various splittings to experiment. Our -results cover a
range in lattice spacings of more than a factor of two. Our -results are
from a single lattice spacing and we compare them to numbers in the literature
from finer lattices using other methods. We see no significant dependence of
physical results on the lattice spacing.
PACS: 11.15.Ha 12.38.Gc 14.40.Lb 14.40.NdComment: 78 pages, 29 tables, 30 figures Revised version. Minor corrections to
spelling and wordin
Charged AdS Black Holes and Catastrophic Holography
We compute the properties of a class of charged black holes in anti-de Sitter
space-time, in diverse dimensions. These black holes are solutions of
consistent Einstein-Maxwell truncations of gauged supergravities, which are
shown to arise from the inclusion of rotation in the transverse space. We
uncover rich thermodynamic phase structures for these systems, which display
classic critical phenomena, including structures isomorphic to the van der
Waals-Maxwell liquid-gas system. In that case, the phases are controlled by the
universal `cusp' and `swallowtail' shapes familiar from catastrophe theory. All
of the thermodynamics is consistent with field theory interpretations via
holography, where the dual field theories can sometimes be found on the world
volumes of coincident rotating branes.Comment: 19 pages, revtex, psfig, 6 multicomponent figures, typos, references
and a few remarks have been repaired, and adde
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