1,098 research outputs found
On Hawking's Local Rigidity Theorems for Charged Black Holes
We show the existence of a Hawking vector field in a full neighborhood of a
local, regular, bifurcate, non-expanding horizon embedded in a smooth
Einstein-Maxwell space-time without assuming the underlying space-time is
analytic. It extends one result of Friedrich, R\'{a}cz and Wald, which was
limited to the interior of the black hole region. Moreover, we also show, in
the presence of an additional Killing vector field which tangent to the
horizon and not vanishing on the bifurcate sphere, then space-time must be
locally axially symmetric without the analyticity assumption. This axial
symmetry plays a fundamental role in the classification theory of stationary
black holes.Comment: 20 page
Covariant Vortex In Superconducting-Superfluid-Normal Fluid Mixtures with Stiff Equation of State
The integrals of motion for a cylindrically symmetric stationary vortex are
obtained in a covariant description of a mixture of interacting
superconductors, superfluids and normal fluids. The relevant integrated
stress-energy coefficients for the vortex with respect to a vortex-free
reference state are calculated in the approximation of a ``stiff'', i.e. least
compressible, relativistic equation of state for the fluid mixture. As an
illustration of the foregoing general results, we discuss their application to
some of the well known examples of ``real'' superfluid and superconducting
systems that are contained as special cases. These include Landau's two-fluid
model, uncharged binary superfluid mixtures, rotating conventional
superconductors and the superfluid neutron-proton-electron plasma in the outer
core of neutron stars.Comment: 14 pages, uses RevTeX and amssymb, submitte
Predictions from Quantum Cosmology
The world view suggested by quantum cosmology is that inflating universes
with all possible values of the fundamental constants are spontaneously created
out of nothing. I explore the consequences of the assumption that we are a
`typical' civilization living in this metauniverse. The conclusions include
inflation with an extremely flat potential and low thermalization temperature,
structure formation by topological defects, and an appreciable cosmological
constant.Comment: (revised version), 15 page
Spectrum of density fluctuations in Brans-Dicke chaotic inflation
In the context of Brans--Dicke theories, eternal inflation is described in
such a way that the evolution of the inflaton field is determined by the value
of the Planck mass in different regions of the universe. The Planck mass is
given by the values of the Brans--Dicke field, which is coupled to the scalar
curvature in the Lagrangian. We first calculate the joint probability
distributions of the inflaton and Brans--Dicke fields, in order to compute the
3--volume ratios of homogeneous regions with arbitrary values of the fields
still undergoing inflation with respect to thermalized regions. From these
volume ratios one is able to extract information on the values of the fields
measured by a typical observer for a given potential and, in particular, the
typical value of the Planck mass at the end of inflation. In this paper, we
investigate volume ratios using a regularization procedure suggested by
Vilenkin, and the results are applied to powerlaw and double--well potentials.
The spectrum of density fluctuations is calculated for generic potentials, and
we discuss the likelihood of various scenarios that could tell us whether our
region of the universe is typical or untypical depending on very general bounds
on the evolution of the Brans--Dicke field.Comment: 26 pages, uuencoded compressed postscript file, two figures include
Stealth Branes
We discuss the brane world model of Dvali, Gabadadze and Porrati in which
branes evolve in an infinite bulk and the brane curvature term is added to the
action. If Z_2 symmetry between the two sides of the brane is not imposed, we
show that the model admits the existence of "stealth branes" which follow the
standard 4D internal evolution and have no gravitational effect on the bulk
space. Stealth branes can nucleate spontaneosly in a Minkowski bulk. This
process is described by the standard 4D quantum cosmology formalism with
tunneling boundary conditions for the brane world wave function. The notorious
ambiguity in the choice of boundary conditions is fixed in this case due to the
presence of the embedding spacetime. We also point to some problematic aspects
of models admitting stealth brane solutions.Comment: 24 pages; Final version, to appear in Phys. Rev. D. The discussion of
"embeddability obstruction" is removed (thanks to Takahiro Tanaka who
convinced us that there is no such obstruction
Agnesi Weighting for the Measure Problem of Cosmology
The measure problem of cosmology is how to assign normalized probabilities to
observations in a universe so large that it may have many observations
occurring at many different spacetime locations. I have previously shown how
the Boltzmann brain problem (that observations arising from thermal or quantum
fluctuations may dominate over ordinary observations if the universe expands
sufficiently and/or lasts long enough) may be ameliorated by volume averaging,
but that still leaves problems if the universe lasts too long. Here a solution
is proposed for that residual problem by a simple weighting factor 1/(1+t^2) to
make the time integral convergent. The resulting Agnesi measure appears to
avoid problems other measures may have with vacua of zero or negative
cosmological constant.Comment: 26 pages, LaTeX; discussion is added of how Agnesi weighting appears
better than other recent measure
Relativistic superfluid models for rotating neutron stars
This article starts by providing an introductory overview of the theoretical
mechanics of rotating neutron stars as developped to account for the frequency
variations, and particularly the discontinuous glitches, observed in pulsars.
The theory suggests, and the observations seem to confirm, that an essential
role is played by the interaction between the solid crust and inner layers
whose superfluid nature allows them to rotate independently. However many
significant details remain to be clarified, even in much studied cases such as
the Crab and Vela. The second part of this article is more technical,
concentrating on just one of the many physical aspects that needs further
development, namely the provision of a satisfactorily relativistic (local but
not microscopic) treatment of the effects of the neutron superfluidity that is
involved.Comment: 42 pages LateX. Contribution to Physics of Neutron Star Interiors,
ed. D. Blasche, N.K. Glendenning, A. Sedrakian (ECT workshop, Trento, June
2000
On the construction of a geometric invariant measuring the deviation from Kerr data
This article contains a detailed and rigorous proof of the construction of a
geometric invariant for initial data sets for the Einstein vacuum field
equations. This geometric invariant vanishes if and only if the initial data
set corresponds to data for the Kerr spacetime, and thus, it characterises this
type of data. The construction presented is valid for boosted and non-boosted
initial data sets which are, in a sense, asymptotically Schwarzschildean. As a
preliminary step to the construction of the geometric invariant, an analysis of
a characterisation of the Kerr spacetime in terms of Killing spinors is carried
out. A space spinor split of the (spacetime) Killing spinor equation is
performed, to obtain a set of three conditions ensuring the existence of a
Killing spinor of the development of the initial data set. In order to
construct the geometric invariant, we introduce the notion of approximate
Killing spinors. These spinors are symmetric valence 2 spinors intrinsic to the
initial hypersurface and satisfy a certain second order elliptic equation
---the approximate Killing spinor equation. This equation arises as the
Euler-Lagrange equation of a non-negative integral functional. This functional
constitutes part of our geometric invariant ---however, the whole functional
does not come from a variational principle. The asymptotic behaviour of
solutions to the approximate Killing spinor equation is studied and an
existence theorem is presented.Comment: 36 pages. Updated references. Technical details correcte
An amplitude analysis of the reaction
A simple partial wave amplitude analysis of has been performed for data in the range p_{\sl lab} = 360 -- 1000
MeV/c. Remarkably few partial waves are required to fit the data, while the
number of required values barely changes over this energy range. However,
the resulting set of partial wave amplitudes is not unique. We discuss possible
measurements with polarized beam and target which will severely restrict and
help resolve the present analysis ambiguities. New data from the reaction
alone, are insufficient for that
purpose.Comment: 16 pages (revtex), 8 figures available on request, submitted to Phys.
Rev.
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