15 research outputs found
Quantum black holes from null expansion operators
Using a recently developed quantization of spherically symmetric gravity
coupled to a scalar field, we give a construction of null expansion operators
that allow a definition of general, fully dynamical quantum black holes. These
operators capture the intuitive idea that classical black holes are defined by
the presence of trapped surfaces, that is surfaces from which light cannot
escape outward. They thus provide a mechanism for classifying quantum states of
the system into those that describe quantum black holes and those that do not.
We find that quantum horizons fluctuate, confirming long-held heuristic
expectations. We also give explicit examples of quantum black hole states. The
work sets a framework for addressing the puzzles of black hole physics in a
fully quantized dynamical setting.Comment: 5 pages, version to appear in CQ
Quantum resolution of black hole singularities
We study the classical and quantum theory of spherically symmetric spacetimes
with scalar field coupling in general relativity. We utilise the canonical
formalism of geometrodynamics adapted to the Painleve-Gullstrand coordinates,
and present a new quantisation of the resulting field theory. We give an
explicit construction of operators that capture curvature properties of the
spacetime and use these to show that the black hole curvature singularity is
avoided in the quantum theory.Comment: 5 pages, version to appear in CQ
Quantum Structure of Space Near a Black Hole Horizon
We describe a midi-superspace quantization scheme for generic single horizon
black holes in which only the spatial diffeomorphisms are fixed. The remaining
Hamiltonian constraint yields an infinite set of decoupled eigenvalue
equations: one at each spatial point. The corresponding operator at each point
is the product of the outgoing and ingoing null convergences, and describes the
scale invariant quantum mechanics of a particle moving in an attractive
potential. The variable that is analoguous to particle position is the
square root of the conformal mode of the metric. We quantize the theory via
Bohr quantization, which by construction turns the Hamiltonian constraint
eigenvalue equation into a finite difference equation. The resulting spectrum
gives rise to a discrete spatial topology exterior to the horizon. The spectrum
approaches the continuum in the asymptotic region.Comment: References added and typos corrected. 21 pages, 1 figur
On (Cosmological) Singularity Avoidance in Loop Quantum Gravity
Loop Quantum Cosmology (LQC), mainly due to Bojowald, is not the cosmological
sector of Loop Quantum Gravity (LQG). Rather, LQC consists of a truncation of
the phase space of classical General Relativity to spatially homogeneous
situations which is then quantized by the methods of LQG. Thus, LQC is a
quantum mechanical toy model (finite number of degrees of freedom) for LQG(a
genuine QFT with an infinite number of degrees of freedom) which provides
important consistency checks. However, it is a non trivial question whether the
predictions of LQC are robust after switching on the inhomogeneous fluctuations
present in full LQG. Two of the most spectacular findings of LQC are that 1.
the inverse scale factor is bounded from above on zero volume eigenstates which
hints at the avoidance of the local curvature singularity and 2. that the
Quantum Einstein Equations are non -- singular which hints at the avoidance of
the global initial singularity. We display the result of a calculation for LQG
which proves that the (analogon of the) inverse scale factor, while densely
defined, is {\it not} bounded from above on zero volume eigenstates. Thus, in
full LQG, if curvature singularity avoidance is realized, then not in this
simple way. In fact, it turns out that the boundedness of the inverse scale
factor is neither necessary nor sufficient for curvature singularity avoidance
and that non -- singular evolution equations are neither necessary nor
sufficient for initial singularity avoidance because none of these criteria are
formulated in terms of observable quantities.After outlining what would be
required, we present the results of a calculation for LQG which could be a
first indication that our criteria at least for curvature singularity avoidance
are satisfied in LQG.Comment: 34 pages, 16 figure
Semiclassical quantisation of space-times with apparent horizons
Coherent or semiclassical states in canonical quantum gravity describe the
classical Schwarzschild space-time. By tracing over the coherent state
wavefunction inside the horizon, a density matrix is derived.
Bekenstein-Hawking entropy is obtained from the density matrix, modulo the
Immirzi parameter. The expectation value of the area and curvature operator is
evaluated in these states. The behaviour near the singularity of the curvature
operator shows that the singularity is resolved. We then generalise the results
to space-times with spherically symmetric apparent horizons.Comment: 52 pages, 4 figure
Production and decay of evolving horizons
We consider a simple physical model for an evolving horizon that is strongly
interacting with its environment, exchanging arbitrarily large quantities of
matter with its environment in the form of both infalling material and outgoing
Hawking radiation. We permit fluxes of both lightlike and timelike particles to
cross the horizon, and ask how the horizon grows and shrinks in response to
such flows. We place a premium on providing a clear and straightforward
exposition with simple formulae.
To be able to handle such a highly dynamical situation in a simple manner we
make one significant physical restriction, that of spherical symmetry, and two
technical mathematical restrictions: (1) We choose to slice the spacetime in
such a way that the space-time foliations (and hence the horizons) are always
spherically symmetric. (2) Furthermore we adopt Painleve-Gullstrand coordinates
(which are well suited to the problem because they are nonsingular at the
horizon) in order to simplify the relevant calculations.
We find particularly simple forms for surface gravity, and for the first and
second law of black hole thermodynamics, in this general evolving horizon
situation. Furthermore we relate our results to Hawking's apparent horizon,
Ashtekar et al's isolated and dynamical horizons, and Hayward's trapping
horizons. The evolving black hole model discussed here will be of interest,
both from an astrophysical viewpoint in terms of discussing growing black
holes, and from a purely theoretical viewpoint in discussing black hole
evaporation via Hawking radiation.Comment: 25 pages, uses iopart.cls V2: 5 references added; minor typos; V3:
some additional clarifications, additional references, additional appendix on
the Viadya spacetime. This version published in Classical and Quiantum
Gravit
Spherically Symmetric Quantum Geometry: Hamiltonian Constraint
Variables adapted to the quantum dynamics of spherically symmetric models are
introduced, which further simplify the spherically symmetric volume operator
and allow an explicit computation of all matrix elements of the Euclidean and
Lorentzian Hamiltonian constraints. The construction fits completely into the
general scheme available in loop quantum gravity for the quantization of the
full theory as well as symmetric models. This then presents a further
consistency check of the whole scheme in inhomogeneous situations, lending
further credence to the physical results obtained so far mainly in homogeneous
models. New applications in particular of the spherically symmetric model in
the context of black hole physics are discussed.Comment: 33 page
Defining breakthrough invasive fungal infection-Position paper of the mycoses study group education and research consortium and the European Confederation of Medical Mycology
Breakthrough invasive fungal infections (IFIs) have emerged as a significant problem in patients receiving systemic antifungals; however, consensus criteria for defining breakthrough IFI are missing. This position paper establishes broadly applicable definitions of breakthrough IFI for clinical research. Representatives of the Mycoses Study Group Education and Research Consortium (MSG-ERC) and the European Confederation of Medical Mycology (ECMM) reviewed the relevant English literature for definitions applied and published through 2018. A draft proposal for definitions was developed and circulated to all members of the two organisations for comment and suggestions. The authors addressed comments received and circulated the updated document for approval. Breakthrough IFI was defined as any IFI occurring during exposure to an antifungal drug, including fungi outside the spectrum of activity of an antifungal. The time of breakthrough IFI was defined as the first attributable clinical sign or symptom, mycological finding or radiological feature. The period defining breakthrough IFI depends on pharmacokinetic properties and extends at least until one dosing interval after drug discontinuation. Persistent IFI describes IFI that is unchanged/stable since treatment initiation with ongoing need for antifungal therapy. It is distinct from refractory IFI, defined as progression of disease and therefore similar to non-response to treatment. Relapsed IFI occurs after treatment and is caused by the same pathogen at the same site, although dissemination can occur. These proposed definitions are intended to support the design of future clinical trials and epidemiological research in clinical mycology, with the ultimate goal of increasing the comparability of clinical trial results