26,584 research outputs found
The golden ratio in Schwarzschild-Kottler black holes
In this paper we show that the golden ratio is present in the
Schwarzschild-Kottler metric. For null geodesics with maximal radial
acceleration, the turning points of the orbits are in the golden ratio . This is a general result which is independent of the value and
sign of the cosmological constant
A redshift survey towards the CMB Cold Spot
We have carried out a redshift survey using the VIMOS spectrograph on the VLT
towards the Cosmic Microwave Background cold spot. A possible cause of the cold
spot is the Integrated Sachs-Wolfe effect imprinted by an extremely large void
(hundreds of Mpc in linear dimension) at intermediate or low redshifts. The
redshift distribution of over seven hundred z<1 emission-line galaxies drawn
from an I-band flux limited sample of galaxies in the direction of the cold
spot shows no evidence of a gap on scales of Delta-z> 0.05 as would be expected
if such a void existed at 0.35<z<1. There are troughs in the redshift
distribution on smaller scales (Delta-z ~0.01) indicating that smaller scale
voids may connect regions separated by several degrees towards the cold spot. A
comparison of this distribution with that generated from similarly-sized
subsamples drawn from widely-spaced pointings of the VVDS survey does not
indicate that the redshift distribution towards the cold spot is anomalous or
that these small gaps can be uniquely attributed to real voids.Comment: MNRAS in press, 6 page
A Cosmic Microwave Background feature consistent with a cosmic texture
The Cosmic Microwave Background provides our most ancient image of the
Universe and our best tool for studying its early evolution. Theories of high
energy physics predict the formation of various types of topological defects in
the very early universe, including cosmic texture which would generate hot and
cold spots in the Cosmic Microwave Background. We show through a Bayesian
statistical analysis that the most prominent, 5 degree radius cold spot
observed in all-sky images, which is otherwise hard to explain, is compatible
with having being caused by a texture. From this model, we constrain the
fundamental symmetry breaking energy scale to be phi_0 ~ 8.7 x 10^(15) GeV. If
confirmed, this detection of a cosmic defect will probe physics at energies
exceeding any conceivable terrestrial experiment.Comment: Accepted by Science. Published electronically via Science Express on
25 October 2007, http://www.sciencemag.org/cgi/content/abstract/114869
Generation of Bright Two-Color Continuous Variable Entanglement
We present the first measurement of squeezed-state entanglement between the
twin beams produced in an Optical Parametric Oscillator (OPO) operating above
threshold. Besides the usual squeezing in the intensity difference between the
twin beams, we have measured squeezing in the sum of phase quadratures. Our
scheme enables us to measure such phase anti-correlations between fields of
different frequencies. In the present measurements, wavelengths differ by ~1
nm. Entanglement is demonstrated according to the Duan et al. criterion [Phys.
Rev. Lett. 84, 2722 (2000)] .
This experiment opens the way for new potential applications such as the
transfer of quantum information between different parts of the electromagnetic
spectrum.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Symmetry Aspects in Nonrelativistic Multi-Scalar Field Models and Application to a Coupled Two-Species Dilute Bose Gas
We discuss unusual aspects of symmetry that can happen due to entropic
effects in the context of multi-scalar field theories at finite temperature. We
present their consequences, in special, for the case of nonrelativistic models
of hard core spheres. We show that for nonrelativistic models phenomena like
inverse symmetry breaking and symmetry non-restoration cannot take place, but a
reentrant phase at high temperatures is shown to be possible for some region of
parameters. We then develop a model of interest in studies of Bose-Einstein
condensation in dilute atomic gases and discuss about its phase transition
patterns. In this application to a Bose-Einstein condensation model, however,
no reentrant phases are found.Comment: 8 pages, 1 eps figure, IOP style. Based on a talk given by R. O.
Ramos at the QFEXT05 workshop, Barcelona, Spain, September 5-9, 2005. One
reference was update
Heart-Kidney Interaction: Epidemiology of Cardiorenal Syndromes
Cardiac and kidney diseases are common, increasingly encountered, and often coexist. Recently, the Acute Dialysis Quality Initiative (ADQI) Working Group convened a consensus conference to develop a classification scheme for the CRS and for five discrete subtypes. These CRS subtypes likely share pathophysiologic mechanisms, however, also have distinguishing clinical features, in terms of precipitating events, risk identification, natural history, and outcomes. Knowledge of the epidemiology of heart-kidney interaction stratified by the proposed CRS subtypes is increasingly important for understanding the overall burden of disease for each CRS subtype, along with associated morbidity, mortality, and health resource utilization. Likewise, an understanding of the epidemiology of CRS is necessary for characterizing whether there exists important knowledge gaps and to aid in the design of clinical studies. This paper will provide a summary of the epidemiology of the cardiorenal syndrome and its subtypes
Static circularly symmetric perfect fluid solutions with an exterior BTZ metric
In this work we study static perfect fluid stars in 2+1 dimensions with an
exterior BTZ spacetime. We found the general expression for the metric
coefficients as a function of the density and pressure of the fluid. We found
the conditions to have regularity at the origin throughout the analysis of a
set of linearly independent invariants. We also obtain an exact solution of the
Einstein equations, with the corresponding equation of state , which
is regular at the origin.Comment: 10 pages, 1 figure, revtex 4. This paper is in honor of Alberto
Garcia's sixtieth birthday. Accepted by Gen. Rel. Gra
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