7,163 research outputs found
Vacuum Polarisation and the Black Hole Singularity
In order to investigate the effects of vacuum polarisation on mass inflation
singularities, we study a simple toy model of a charged black hole with cross
flowing radial null dust which is homogeneous in the black hole interior. In
the region we find an approximate analytic solution to the
classical field equations. The renormalized stress-energy tensor is evaluated
on this background and we find the vacuum polarisation backreaction corrections
to the mass function . Asymptotic analysis of the semiclassical mass
function shows that the mass inflation singularity is much stronger in the
presence of vacuum polarisation than in the classical case.Comment: 12 pages, RevTe
Cosmic Censorship: As Strong As Ever
Spacetimes which have been considered counter-examples to strong cosmic
censorship are revisited. We demonstrate the classical instability of the
Cauchy horizon inside charged black holes embedded in de Sitter spacetime for
all values of the physical parameters. The relevant modes which maintain the
instability, in the regime which was previously considered stable, originate as
outgoing modes near to the black hole event horizon. This same mechanism is
also relevant for the instability of Cauchy horizons in other proposed
counter-examples of strong cosmic censorship.Comment: 4 pages RevTeX style, 1 figure included using epsfi
LISA data analysis: The monochromatic binary detection and initial guess problems
We consider the detection and initial guess problems for the LISA
gravitational wave detector. The detection problem is the problem of how to
determine if there is a signal present in instrumental data and how to identify
it. Because of the Doppler and plane-precession spreading of the spectral power
of the LISA signal, the usual power spectrum approach to detection will have
difficulty identifying sources. A better method must be found. The initial
guess problem involves how to generate {\it a priori} values for the parameters
of a parameter-estimation problem that are close enough to the final values for
a linear least-squares estimator to converge to the correct result. A useful
approach to simultaneously solving the detection and initial guess problems for
LISA is to divide the sky into many pixels and to demodulate the Doppler
spreading for each set of pixel coordinates. The demodulated power spectra may
then be searched for spectral features. We demonstrate that the procedure works
well as a first step in the search for gravitational waves from monochromatic
binaries.Comment: 8 pages, 8 figure
Black hole formation from massive scalar fields
It is shown that there exists a range of parameters in which gravitational
collapse with a spherically symmetric massive scalar field can be treated as if
it were collapsing dust. This implies a criterion for the formation of black
holes depending on the size and mass of the initial field configuration and the
mass of the scalar field.Comment: 11 pages, RevTeX, 3 eps figures. Submitted to Class. Quantum Gra
Distribution of the birds of the Philippines: biogeography and conservation priorities
The Philippine islands hold a concentration of species diversity and endemism of global
importance, yet few studies have analyzed biogeographic patterns or attempted to
prioritize areas for conservation within the archipelago. We analyzed distributions of 386
species on 28 Philippine islands and island groups, documenting intense concentration of
species richness, especially of endemic species, on the two largest islands, Mindanao and
Luzon. Factors identified as influencing species richness included island area, maximum
elevation, and Pleistocene patterns of connection and isolation. Reserve systems were
developed based on heuristic complementarity algorithms, and compared with the
existing Integrated Protected Areas (IPAS) system in the country, showing that IPAS is
an impressive first step towards protecting avian diversity in the country. Addition of
presently proposed reserves on Palawan and Mindoro would make IPAS a near-optimal
reserve design, at least at the level of island representation. Important challenges remain,
however, with regard to design of reserve systems within islands to represent complete
island avifaunas
Quantum Effects in Black Hole Interiors
The Weyl curvature inside a black hole formed in a generic collapse grows,
classically without bound, near to the inner horizon, due to partial absorption
and blueshifting of the radiative tail of the collapse. Using a spherical
model, we examine how this growth is modified by quantum effects of conformally
coupled massless fields.Comment: 13 pages, 1 figure (not included), RevTe
Conductance Fluctuations of Generic Billiards: Fractal or Isolated?
We study the signatures of a classical mixed phase space for open quantum
systems. We find the scaling of the break time up to which quantum mechanics
mimics the classical staying probability and derive the distribution of
resonance widths. Based on these results we explain why for mixed systems two
types of conductance fluctuat ions were found: quantum mechanics divides the
hierarchically structured chaotic component of phase space into two parts - one
yields fractal conductance fluctuations while the other causes isolated
resonances. In general, both types appear together, but on different energy
scales.Comment: restructured and new figure
Do naked singularities generically occur in generalized theories of gravity?
A new mechanism for causing naked singularities is found in an effective
superstring theory. We investigate the gravitational collapse in a spherically
symmetric Einstein-Maxwell-dilaton system in the presence of a pure
cosmological constant "potential", where the system has no static black hole
solution. We show that once gravitational collapse occurs in the system, naked
singularities necessarily appear in the sense that the field equations break
down in the domain of outer communications. This suggests that in generalized
theories of gravity, the non-minimally coupled fields generically cause naked
singularities in the process of gravitational collapse if the system has no
static or stationary black hole solution.Comment: 4 pages including 2 eps figures, to be published in Physical Review
Letter
A Cosmological No-Hair Theorem
A generalisation of Price's theorem is given for application to Inflationary
Cosmologies. Namely, we show that on a Schwarzschild--de Sitter background
there are no static solutions to the wave or gravitational perturbation
equations for modes with angular momentum greater than their intrinsic spin.Comment: 9 pages, NCL94 -TP4, (Revtex
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