4,182 research outputs found
Cosmic Growth History and Expansion History
The cosmic expansion history tests the dynamics of the global evolution of
the universe and its energy density contents, while the cosmic growth history
tests the evolution of the inhomogeneous part of the energy density. Precision
comparison of the two histories can distinguish the nature of the physics
responsible for the accelerating cosmic expansion: an additional smooth
component - dark energy - or a modification of the gravitational field
equations. With the aid of a new fitting formula for linear perturbation growth
accurate to 0.05-0.2%, we separate out the growth dependence on the expansion
history and introduce a new growth index parameter \gamma that quantifies the
gravitational modification.Comment: 8 pages, 3 figures; minor changes to match version accepted to PR
Gravitational Wave Sirens as a Triple Probe of Dark Energy
Gravitational wave standard sirens have been considered as precision distance
indicators to high redshift; however, at high redshift standard sirens or
standard candles such as supernovae suffer from lensing noise. We investigate
lensing noise as a signal instead and show how measurements of the maximum
demagnification (minimum convergence) probe cosmology in a highly complementary
manner to the distance itself. Revisiting the original form for minimum
convergence we quantify the bias arising from the commonly used approximation.
Furthermore, after presenting a new lensing probability function we discuss how
the width of the lensed standard siren amplitude distribution also probes
growth of structure. Thus standard sirens and candles can serve as triple
probes of dark energy, measuring both the cosmic expansion history and growth
history.Comment: 7 pages, 5 figures; v2 minor changes matching published versio
Spontaneously Localized Photonic Modes Due to Disorder in the Dielectric Constant
We present the first experimental evidence for the existence of strongly
localized photonic modes due to random two dimensional fluctuations in the
dielectric constant. In one direction, the modes are trapped by ordered Bragg
reflecting mirrors of a planar, one wavelength long, microcavity. In the cavity
plane, they are localized by disorder, which is due to randomness in the
position, composition and sizes of quantum dots located in the anti-node of the
cavity. We extend the theory of disorder induced strong localization of
electron states to optical modes and obtain quantitative agreement with the
main experimental observations.Comment: 6 page
Comparison of organoleptic acceptability of liquid and fresh diets
Organoleptic acceptability of liquid and fresh diets for space flight feedin
Cosmology with X-ray Cluster Baryons
X-ray cluster measurements interpreted with a universal baryon/gas mass
fraction can theoretically serve as a cosmological distance probe. We examine
issues of cosmological sensitivity for current (e.g. Chandra X-ray Observatory,
XMM-Newton) and next generation (e.g. Con-X, XEUS) observations, along with
systematic uncertainties and biases. To give competitive next generation
constraints on dark energy, we find that systematics will need to be controlled
to better than 1% and any evolution in f_gas (and other cluster gas properties)
must be calibrated so the residual uncertainty is weaker than (1+z)^{0.03}.Comment: 6 pages, 5 figures; v2: 13 pages, substantial elaboration and
reordering, matches JCAP versio
Spin-triplet Supercurrent through Inhomogeneous Ferromagnetic Trilayers
Motivated by a recent experiment [J. W. A. Robinson, J. D. S. Witt and M. G.
Blamire, Science, \textbf{329}, 5987 (2010)], we here study the possibility of
establishing a long-range spin-triplet supercurrent through an inhomogeneous
ferromagnetic region consisting of a HoCoHo trilayer sandwiched
between two conventional s-wave superconductors. We utilize a full numerical
solution in the diffusive regime of transport and study the behavior of the
supercurrent for various experimentally relevant configurations of the
ferromagnetic trilayer. We obtain qualitatively very good agreement with
experimental data regarding the behavior of the supercurrent as a function of
the width of the Co-layer, . Moreover, we find a synthesis of
0- oscillations with superimposed rapid oscillations when varying the
width of the Ho-layer which pertain specifically to the spiral magnetization
texture in Ho. We are not able to reproduce the anomalous peaks in the
supercurrent observed experimentally in this regime, but note that the results
obtained are quite sensitive to the exact magnetization profile in the
Ho-layers, which could be the reason for the discrepancy between our model and
the experimental reported data for this particular aspect. We also investigate
the supercurrent in a system where the intrinsically inhomogeneous Ho
ferromagnets are replaced with domain-wall ferromagnets, and find similar
behavior as in the HoCoHo case. Furthermore, we propose a novel
type of magnetic Josephson junction including only a domain-wall ferromagnet
and a homogeneous ferromagnetic layer, which in addition to simplicity
regarding the magnetization profile also offers a tunable long-range
spin-triplet supercurrent. Finally, we discuss some experimental aspects of our
findings.Comment: 7 pages, 7 figures. Submitted to Physical Revie
Optimal strategies : theoretical approaches to the parametrization of the dark energy equation of state
The absence of compelling theoretical model requires the parameterizing the
dark energy to probe its properties. The parametrization of the equation of
state of the dark energy is a common method. We explore the theoretical
optimization of the parametrization based on the Fisher information matrix. As
a suitable parametrization, it should be stable at high redshift and should
produce the determinant of the Fisher matrix as large as possible. For the
illustration, we propose one parametrization which can satisfy both criteria.
By using the proper parametrization, we can improve the constraints on the dark
energy even for the same data. We also show the weakness of the so-called
principal component analysis method.Comment: 7pages, 11 figures, 2 tables, To match the version accepted by AS
Dynamics and constraints of the Unified Dark Matter flat cosmologies
We study the dynamics of the scalar field FLRW flat cosmological models
within the framework of the Unified Dark Matter (UDM) scenario. In this model
we find that the main cosmological functions such as the scale factor of the
Universe, the scalar field, the Hubble flow and the equation of state parameter
are defined in terms of hyperbolic functions. These analytical solutions can
accommodate an accelerated expansion, equivalent to either the dark energy or
the standard models. Performing a joint likelihood analysis of the
recent supernovae type Ia data and the Baryonic Acoustic Oscillations traced by
the SDSS galaxies, we place tight constraints on the main cosmological
parameters of the UDM cosmological scenario. Finally, we compare the UDM
scenario with various dark energy models namely cosmology, parametric
dark energy model and variable Chaplygin gas. We find that the UDM scalar field
model provides a large and small scale dynamics which are in fair agreement
with the predictions by the above dark energy models although there are some
differences especially at high redshifts.Comment: 11 pages, 7 figures, published in Physical Review D, 78, 083509,
(2008
Quinstant Dark Energy Predictions for Structure Formation
We explore the predictions of a class of dark energy models, quinstant dark
energy, concerning the structure formation in the Universe, both in the linear
and non-linear regimes. Quinstant dark energy is considered to be formed by
quintessence and a negative cosmological constant. We conclude that these
models give good predictions for structure formation in the linear regime, but
fail to do so in the non-linear one, for redshifts larger than one.Comment: 9 pages, 14 figures, "Accepted for publication in Astrophysics &
Space Science
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