4,153 research outputs found
Axisymmetric electrovacuum spacetimes with a translational Killing vector at null infinity
By using the Bondi-Sachs-van der Burg formalism we analyze the asymptotic
properties at null infinity of axisymmetric electrovacuum spacetimes with a
translational Killing vector and, in general, an infinite ``cosmic string''
(represented by a conical singularity) along the axis. Such spacetimes admit
only a local null infinity. There is a non-vanishing news function due to the
existence of the string even though there is no radiation.
We prove that if null infinity has a smooth compact cross section and the
spacetime is not flat in a neighbourhood of null infinity, then the
translational Killing vector must be timelike and the spacetime is stationary.
The other case in which an additional symmetry of axisymmetric spacetimes
admits compact cross sections of null infinity is the boost symmetry, which
leads to radiative spacetimes representing ``uniformly accelerated objects''.
These cases were analyzed in detail in our previous works. If the translational
Killing vector is spacelike or null, corresponding to cylindrical or plane
waves, some complete generators of null infinity are ``singular'' but null
infinity itself can be smooth apart from these generators.
As two explicit examples of local null infinity, Schwarzschild spacetime with
a string and a class of cylindrical waves with a string are discussed in detail
in the Appendix.Comment: 15 pages, RevTeX, submitted to Class. Quantum Gra
The spherical symmetry Black hole collapse in expanding universe
The spherical symmetry Black holes are considered in expanding background.
The singularity line and the marginally trapped tube surface behavior are
discussed. In particular, we address the conditions whether dynamical horizon
forms for these cosmological black holes. We also discuss about the
cosmological constant effect on these black hole and the redshift of the light
which comes from the marginally trapped tube surface.Comment: 7 pages, 3 figures. Accepted for publication in International Journal
of Modern Physics D (IJMPD). arXiv admin note: text overlap with
arXiv:gr-qc/0308033 and arXiv:gr-qc/030611
Don\u27t Tread on Me: Has the United States Government\u27s Quest for Customer Records from UBS Sounded the Death Knell for Swiss Bank Secrecy Laws
Privacy protection is a defining characteristic of Swiss culture and a pillar of the Swiss economy. For centuries, the Swiss people have coveted the principles of individual privacy, regularly reaffirming those principles in response to referendums designed to limit them. Swiss banking secrecy, one aspect of privacy, is protected by Swiss criminal and civil laws and professional duties. Swiss banks pride themselves on protecting customer identity and have leveraged their legal and cultural commitment to secrecy to gain a competitive advantage in the global banking market. This brief Article discusses the Swiss banking laws that prohibit a Swiss bank from disclosing client information even if those Swiss laws are at odds with United States law. The Article then provides an overview of the UBS matter. Finally, the Article briefly analyzes the UBS dispute over the account information under a conflicts of law framework to hypothesize on the outcome had the matter been decided by the court. Analyzing the UBS dispute may prove useful in predicting the outcome of inevitable future disputes between the United States government and global banks over confidential client information
Gravitational Waves in the Nonsymmetric Gravitational Theory
We prove that the flux of gravitational radiation from an isolated source in
the Nonsymmetric Gravitational Theory is identical to that found in Einstein's
General Theory of Relativity.Comment: 10 Page
On the Magnitude of Dark Energy Voids and Overdensities
We investigate the clustering of dark energy within matter overdensities and
voids. In particular, we derive an analytical expression for the dark energy
density perturbations, which is valid both in the linear, quasi-linear and
fully non-linear regime of structure formation. We also investigate the
possibility of detecting such dark energy clustering through the ISW effect. In
the case of uncoupled quintessence models, if the mass of the field is of order
the Hubble scale today or smaller, dark energy fluctuations are always small
compared to the matter density contrast. Even when the matter perturbations
enter the non-linear regime, the dark energy perturbations remain linear. We
find that virialised clusters and voids correspond to local overdensities in
dark energy, with \delta_{\phi}/(1+w) \sim \Oo(10^{-5}) for voids,
\delta_{\phi}/(1+w) \sim \Oo(10^{-4}) for super-voids and
\delta_{\phi}/(1+w) \sim \Oo(10^{-5}) for a typical virialised cluster. If
voids with radii of exist within the visible Universe then
may be as large as . Linear overdensities of
matter and super-clusters generally correspond to local voids in dark energy;
for a typical super-cluster: \delta_{\phi}/(1+w) \sim \Oo(-10^{-5}). The
approach taken in this work could be straightforwardly extended to study the
clustering of more general dark energy models.Comment: 20 pages, 14 figures. Accepted by the Astrophys.
Killing vectors and anisotropy
We consider an action that can generate fluids with three unequal stresses
for metrics with a spacelike Killing vector. The parameters in the action are
directly related to the stress anisotropies. The field equations following from
the action are applied to an anisotropic cosmological expansion and an
extension of the Gott-Hiscock cosmic string
Laudatores Temporis Acti, or Why Cosmology is Alive and Well - A Reply to Disney
A recent criticism of cosmological methodology and achievements by Disney
(2000) is assessed. Some historical and epistemological fallacies in the said
article have been highlighted. It is shown that---both empirically and
epistemologically---modern cosmology lies on sounder foundations than it is
portrayed. A brief historical account demonstrates that this form of
unsatisfaction with cosmology has had a long tradition, and rather meagre
results in the course of the XX century.Comment: 11 pages, no figures; a criticism of astro-ph/0009020; Gen. Rel.
Grav., accepted for publicatio
Wiggles in the cosmic microwave background radiation: echoes from non-singular cyclic-inflation
In this paper we consider a unique model of inflation where the universe
undergoes rapid asymmetric oscillations, each cycle lasting millions of Planck
time. Over many-many cycles the space-time expands to mimic the standard
inflationary scenario. Moreover, these rapid oscillations leave a distinctive
periodic signature in ln(k) in the primordial power spectrum, where k denotes
the comoving scale. The best fit parameters of the cyclic-inflation model
provides a very good fit to the 7-year WMAP data.Comment: Computational details and a figure adde
The stellar mass-accretion rate relation in T Tauri stars and brown dwarfs
Recent observations show a strong correlation between stellar mass and
accretion rate in young stellar and sub-stellar objects, with the scaling
holding over more than four orders of magnitude
in accretion rate. We explore the consequences of this correlation in the
context of disk evolution models. We note that such a correlation is not
expected to arise from variations in disk angular momentum transport efficiency
with stellar mass, and suggest that it may reflect a systematic trend in disk
initial conditions. In this case we find that brown dwarf disks initially have
rather larger radii than those around more massive objects. By considering disk
evolution, and invoking a simple parametrization for a shut-off in accretion at
the end of the disk lifetime, we show that such models predict that the scatter
in the stellar mass-accretion rate relationship should increase with increasing
stellar mass, in rough agreement with current observations.Comment: 4 pages, 2 figures. Accepted for publication in ApJ Letter
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