61 research outputs found
Bose Condensation and the BTZ Black Hole
Although all popular approaches to quantum gravity are able to recover the
Bekenstein-Hawking entropy-area law in the thermodynamic limit, there are
significant differences in their descriptions of the microstates and in the
application of statistics. Therefore they can have significantly different
phenomenological implications. For example, requiring indistinguishability of
the elementary degrees of freedom should lead to changes in the black hole's
radiative porperties away from the thermodynamic limit and at low temperatures.
We demonstrate this for the Ba\~nados-Teitelboim-Zanelli (BTZ) black hole. The
energy eigenstates and statistical entropy in the thermodynamic limit of the
BTZ black hole were obtained earlier by us via symmetry reduced canonical
quantum gravity. In that model the BTZ black hole behaves as a system of
Bosonic mass shells moving in a one dimensional harmonic trap. Bose
condensation does not occur in the thermodynamic limit but this system
possesses a finite critical temperature, , and exhibits a large condensate
fraction below when the number of shells is finite.Comment: 5 pages, 5 figures. Published versio
Modified dispersion relations and the response of the rotating Unruh-DeWitt detector
We study the response of a rotating monopole detector that is coupled to a
massless scalar field which is described by a non-linear dispersion relation in
flat spacetime. Since it does not seem to be possible to evaluate the response
of the rotating detector analytically, we resort to numerical computations.
Interestingly, unlike the case of the uniformly accelerated detector that has
been considered recently, we find that defining the transition probability rate
of the rotating detector poses no difficulties. Further, we show that the
response of the rotating detector can be computed {\it exactly}\vee (albeit,
numerically) even when it is coupled to a field that is governed by a
non-linear dispersion relation. We also discuss the response of the rotating
detector in the presence of a cylindrical boundary on which the scalar field is
constrained to vanish. While super-luminal dispersion relations hardly affect
the standard results, we find that sub-luminal dispersion relations can lead to
relatively large modifications.Comment: V1: 11 pages, 3 figures; V2: 12 pages, 3 figures, considerably
revised, we now calculate the detector response exactly; V3: 14 pages, 3
figures, minor changes, to appear in Phys. Rev.
Gravitational Collapse of Inhomogeneous Dust in (2+1) Dimensions
We examine the gravitational collapse of spherically symmetric inhomogeneous
dust in (2+1) dimensions, with cosmological constant. We obtain the analytical
expressions for the interior metric. We match the solution to a vacuum
exterior. We discuss the nature of the singularity formed by analyzing the
outgoing radial null geodesics. We examine the formation of trapped surfaces
during the collapse.Comment: Accepted for publication in CQ
Cosmology in three dimensions: steps towards the general solution
We use covariant and first-order formalism techniques to study the properties
of general relativistic cosmology in three dimensions. The covariant approach
provides an irreducible decomposition of the relativistic equations, which
allows for a mathematically compact and physically transparent description of
the 3-dimensional spacetimes. Using this information we review the features of
homogeneous and isotropic 3-d cosmologies, provide a number of new solutions
and study gauge invariant perturbations around them. The first-order formalism
is then used to provide a detailed study of the most general 3-d spacetimes
containing perfect-fluid matter. Assuming the material content to be dust with
comoving spatial 2-velocities, we find the general solution of the Einstein
equations with non-zero (and zero) cosmological constant and generalise known
solutions of Kriele and the 3-d counterparts of the Szekeres solutions. In the
case of a non-comoving dust fluid we find the general solution in the case of
one non-zero fluid velocity component. We consider the asymptotic behaviour of
the families of 3-d cosmologies with rotation and shear and analyse their
singular structure. We also provide the general solution for cosmologies with
one spacelike Killing vector, find solutions for cosmologies containing scalar
fields and identify all the PP-wave 2+1 spacetimes.Comment: 35 pages, 2 figure
Classical and Quantum Gravitational Collapse in d-dim AdS Spacetime I. Classical Solutions
We study the collapse of a spherically symmetric dust distribution in
-dimensional AdS spacetime. We investigate the role of dimensionality, and
the presence of a negative cosmological constant, in determining the formation
of trapped surfaces and the end state of gravitational collapse. We obtain the
self-similar solution for the case of zero cosmological constant, and show that
one cannot construct a self-similar solution when a cosmological constant is
included.Comment: 19 pages, sections on surface gravity removed, section on self
similar solution expanded, appendix removed, references added. To appear in
Phys. Rev.
Albuterol metered dose inhaler performance under hyperbaric pressures
Comparative Medicine - OneHealth and Comparative Medicine Poster SessionINTRODUCTION: The stimulus for this presentation was an asthma attack suffered on the first dive by a victim of a severe industrial electrical burn. The patient's response to albuterol metered dose inhaler (MDI) treatment given at depth was felt to have been poor. We thus wondered what the output of these devises (chlorofluorocarbon or CFC) was at therapeutic depth versus normobaria. As the current MDIs were being phased out of use we also wondered what the comparable output characteristics of the replacement MDIs (hydrofluoroalkane or HFA) would be.
MATERIALS AND METHODS: The dose and aerosol particle size and number delivered by MDIs were measured in a hyperbaric chamber at pressures ranging from one atmosphere absolute (1 ATA, 0 feet of seawater, fsw, 101 kPa) to three ATA (66 fsw, 304 kPa). Mass delivered was measured by a Sartorius B120 analytical balance, and particle size analysis by a TSI 3080L electrostatic classifier with a TSI 3776 ultrafine condensation particle counter.
RESULTS: Dose delivery per actuation by CFC and long canister HFA powered MDIs was 13±1% and 12±1% less, respectively, at 3 ATA compared to 1 ATA. However, dose delivery by short canister HFA MDIs was not significantly changed with pressure. The geometric mean diameters of nano particles from the CFC and short canister HFA MDIs decreased from 50 nm at 0 fsw to 32 nm at 66 fsw whereas the long canister HFA aerosol diameters were not affected. The numbers of nanometer size particles delivered at 66 fsw were only 4-7% of those delivered at 0 fsw for the CFC and long canister HFA MDIs; whereas for the short canister HFAs it was 26%.
CONCLUSIONS: The doses of albuterol and the sizes and numbers of aerosol particles emitted from albuterol MDIs actuated in a hyperbaric environment vary by canister type; CFC MDI loss is probably unimportant
Dynamical formation and evolution of (2+1)-dimensional charged black holes
In this paper, we investigate the dynamical formation and evolution of 2 +
1-dimensional charged black holes. We numerically study dynamical collapses of
charged matter fields in an anti de Sitter background and note the formation of
black holes using the double-null formalism. Moreover, we include re-normalized
energy-momentum tensors assuming the S-wave approximation to determine
thermodynamical back-reactions to the internal structures. If there is no
semi-classical effects, the amount of charge determines the causal structures.
If the charge is sufficiently small, the causal structure has a space-like
singularity. However, as the charge increases, an inner Cauchy horizon appears.
If we have sufficient charge, we see a space-like outer horizon and a time-like
inner horizon, and if we give excessive charge, black hole horizons disappear.
We have some circumstantial evidences that weak cosmic censorship is still
satisfied, even for such excessive charge cases. Also, we confirm that there is
mass inflation along the inner horizon, although the properties are quite
different from those of four-dimensional cases. Semi-classical back-reactions
will not affect the outer horizon, but they will affect the inner horizon. Near
the center, there is a place where negative energy is concentrated. Thus,
charged black holes in three dimensions have two types of curvature
singularities in general: via mass inflation and via a concentration of
negative energy. Finally, we classify possible causal structures.Comment: 40 pages, 15 figure
Canonical Quantization of Spherically Symmetric Dust Collapse
Quantum gravity effects are likely to play a crucial role in determining the
outcome of gravitational collapse during its final stages. In this contribution
we will outline a canonical quantization of the LeMaitre-Tolman-Bondi models,
which describe the collapse of spherical, inhomogeneous, non-rotating dust.
Although there are many models of gravitational collapse, this particular class
of models stands out for its simplicity and the fact that both black holes and
naked singularity end states may be realized on the classical level, depending
on the initial conditions. We will obtain the appropriate Wheeler-DeWitt
equation and then solve it exactly, after regularization on a spatial lattice.
The solutions describe Hawking radiation and provide an elegant microcanonical
description of black hole entropy, but they raise other questions, most
importantly concerning the nature of gravity's fundamental degrees of freedom.Comment: 19 pages no figures. Contribution to a festschrift in honor of Joshua
N. Goldber
Naked Singularity Formation In f(R) Gravity
We study the gravitational collapse of a star with barotropic equation of
state in the context of theories of gravity.
Utilizing the metric formalism, we rewrite the field equations as those of
Brans-Dicke theory with vanishing coupling parameter. By choosing the
functionality of Ricci scalar as , we
show that for an appropriate initial value of the energy density, if
and satisfy certain conditions, the resulting singularity would be naked,
violating the cosmic censorship conjecture. These conditions are the ratio of
the mass function to the area radius of the collapsing ball, negativity of the
effective pressure, and the time behavior of the Kretschmann scalar. Also, as
long as parameter obeys certain conditions, the satisfaction of the
weak energy condition is guaranteed by the collapsing configuration.Comment: 15 pages, 4 figures, to appear in GR
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