506 research outputs found
Cosmological Information in Weak Lensing Peaks
Recent studies have shown that the number counts of convergence peaks
N(kappa) in weak lensing (WL) maps, expected from large forthcoming surveys,
can be a useful probe of cosmology. We follow up on this finding, and use a
suite of WL convergence maps, obtained from ray-tracing N-body simulations, to
study (i) the physical origin of WL peaks with different heights, and (ii)
whether the peaks contain information beyond the convergence power spectrum
P_ell. In agreement with earlier work, we find that high peaks (with amplitudes
>~ 3.5 sigma, where sigma is the r.m.s. of the convergence kappa) are typically
dominated by a single massive halo. In contrast, medium-height peaks (~0.5-1.5
sigma) cannot be attributed to a single collapsed dark matter halo, and are
instead created by the projection of multiple (typically, 4-8) halos along the
line of sight, and by random galaxy shape noise. Nevertheless, these peaks
dominate the sensitivity to the cosmological parameters w, sigma_8, and
Omega_m. We find that the peak height distribution and its dependence on
cosmology differ significantly from predictions in a Gaussian random field. We
directly compute the marginalized errors on w, sigma_8, and Omega_m from the
N(kappa) + P_ell combination, including redshift tomography with source
galaxies at z_s=1 and z_s=2. We find that the N(kappa) + P_ell combination has
approximately twice the cosmological sensitivity compared to P_ell alone. These
results demonstrate that N(kappa) contains non-Gaussian information
complementary to the power spectrum.Comment: 24 pages, 12 figures, 14 tables. Accepted for publication in PRD
(version before proofs
Sustainability assessment of organic dairy farms in mountainous areas of Austria
Dairy farming plays a major role in mountainous regions of Austria, mostly due to high proportion of grasslands. In general, Austria’s dairy farming faces challenges regarding sustainability, e.g. environmental impacts, but specifically for alpine areas low productivity and dependency on direct payments are lowering sustainability. Organic farming is considered as a strategy to overcome these challenges.
Considering this general background, we analysed the sustainability performance and its main drivers of organic dairy farms in mountainous regions of Austria
Probing the time dependence of dark energy
A new method to investigate a possible time-dependence of the dark energy
equation of state is proposed. We apply this methodology to two of the most
recent data sets of type Ia supernova (Union2 and SDSS) and the baryon acoustic
oscillation peak at . For some combinations of these data, we show
that there is a clear departure from the standard CDM model at
intermediary redshifts, although a non-evolving dark energy component () cannot be ruled out by these data. The approach developed here may be
useful to probe a possible evolving dark energy component when applied to
upcoming observational data.Comment: 6 pages, 3 figures, LaTe
Probing Cosmology with Weak Lensing Minkowski Functionals
In this paper, we show that Minkowski Functionals (MFs) of weak gravitational
lensing (WL) convergence maps contain significant non-Gaussian,
cosmology-dependent information. To do this, we use a large suite of
cosmological ray-tracing N-body simulations to create mock WL convergence maps,
and study the cosmological information content of MFs derived from these maps.
Our suite consists of 80 independent 512^3 N-body runs, covering seven
different cosmologies, varying three cosmological parameters Omega_m, w, and
sigma_8 one at a time, around a fiducial LambdaCDM model. In each cosmology, we
use ray-tracing to create a thousand pseudo-independent 12 deg^2 convergence
maps, and use these in a Monte Carlo procedure to estimate the joint confidence
contours on the above three parameters. We include redshift tomography at three
different source redshifts z_s=1, 1.5, 2, explore five different smoothing
scales theta_G=1, 2, 3, 5, 10 arcmin, and explicitly compare and combine the
MFs with the WL power spectrum. We find that the MFs capture a substantial
amount of information from non-Gaussian features of convergence maps, i.e.
beyond the power spectrum. The MFs are particularly well suited to break
degeneracies and to constrain the dark energy equation of state parameter w (by
a factor of ~ three better than from the power spectrum alone). The
non-Gaussian information derives partly from the one-point function of the
convergence (through V_0, the "area" MF), and partly through non-linear spatial
information (through combining different smoothing scales for V_0, and through
V_1 and V_2, the boundary length and genus MFs, respectively). In contrast to
the power spectrum, the best constraints from the MFs are obtained only when
multiple smoothing scales are combined.Comment: 19 pages, 9 figures, 5 table
Black hole production in tachyonic preheating
We present fully non-linear simulations of a self-interacting scalar field in
the early universe undergoing tachyonic preheating. We find that density
perturbations on sub-horizon scales which are amplified by tachyonic
instability maintain long range correlations even during the succeeding
parametric resonance, in contrast to the standard models of preheating
dominated by parametric resonance. As a result the final spectrum exhibits
memory and is not universal in shape. We find that throughout the subsequent
era of parametric resonance the equation of state of the universe is almost
dust-like, hence the Jeans wavelength is much smaller than the horizon scale.
If our 2D simulations are accurate reflections of the situation in 3D, then
there are wide regions of parameter space ruled out by over-production of black
holes. It is likely however that realistic parameter values, consistent with
COBE/WMAP normalisation, are safetly outside this black hole over-production
region.Comment: 6pages, 7figures, figures correcte
Jerk, snap, and the cosmological equation of state
Taylor expanding the cosmological equation of state around the current epoch
is the simplest model one can consider that does not make any a priori
restrictions on the nature of the cosmological fluid. Most popular cosmological
models attempt to be ``predictive'', in the sense that once somea priori
equation of state is chosen the Friedmann equations are used to determine the
evolution of the FRW scale factor a(t). In contrast, a retrodictive approach
might usefully take observational dataconcerning the scale factor, and use the
Friedmann equations to infer an observed cosmological equation of state. In
particular, the value and derivatives of the scale factor determined at the
current epoch place constraints on the value and derivatives of the
cosmological equation of state at the current epoch. Determining the first
three Taylor coefficients of the equation of state at the current epoch
requires a measurement of the deceleration, jerk, and snap -- the second,
third, and fourth derivatives of the scale factor with respect to time.
Higher-order Taylor coefficients in the equation of state are related to
higher-order time derivatives of the scale factor. Since the jerk and snap are
rather difficult to measure, being related to the third and fourth terms in the
Taylor series expansion of the Hubble law, it becomes clear why direct
observational constraints on the cosmological equation of state are so
relatively weak; and are likely to remain weak for the foreseeable future.Comment: V1: 10 pages; uses iopart.cls setstack.sty V2: six additional
references, some clarifying comments and discussion, no physics changes. V3:
significant additions based on community feedback; explicit calculations now
carried out to fourth order in redshift. V4: Discussion of current
observational situation added. This version accepted for publication in
Classical and Quantum Gravity. Now 15 page
Interpolating Masked Weak Lensing Signal with Karhunen-Loeve Analysis
We explore the utility of Karhunen Loeve (KL) analysis in solving practical
problems in the analysis of gravitational shear surveys. Shear catalogs from
large-field weak lensing surveys will be subject to many systematic
limitations, notably incomplete coverage and pixel-level masking due to
foreground sources. We develop a method to use two dimensional KL eigenmodes of
shear to interpolate noisy shear measurements across masked regions. We explore
the results of this method with simulated shear catalogs, using statistics of
high-convergence regions in the resulting map. We find that the KL procedure
not only minimizes the bias due to masked regions in the field, it also reduces
spurious peak counts from shape noise by a factor of ~ 3 in the cosmologically
sensitive regime. This indicates that KL reconstructions of masked shear are
not only useful for creating robust convergence maps from masked shear
catalogs, but also offer promise of improved parameter constraints within
studies of shear peak statistics.Comment: 13 pages, 9 figures; submitted to Ap
Testing the Cosmological Constant as a Candidate for Dark Energy
It may be difficult to single out the best model of dark energy on the basis
of the existing and planned cosmological observations, because many different
models can lead to similar observational consequences. However, each particular
model can be studied and either found consistent with observations or ruled
out. In this paper, we concentrate on the possibility to test and rule out the
simplest and by far the most popular of the models of dark energy, the theory
described by general relativity with positive vacuum energy (the cosmological
constant). We evaluate the conditions under which this model could be ruled out
by the future observations made by the Supernova/Acceleration Probe SNAP (both
for supernovae and weak lensing) and by the Planck Surveyor cosmic microwave
background satellite.Comment: 6 pages, 2 figures, revtex
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Photovoltaic module performance and durability following long-term field exposure
Our investigations of both new and field-aged photovoltaic modules have indicated that, in general, today's commercially available modules area highly reliable product. However, by using new test procedures, subtle failure mechanisms have also been identified that must be addressed in order to achieve 30-year module lifetimes. This paper summarizes diagnostic test procedures, results, and implications of in-depth investigations of the performance and durability characteristics of commercial modules after long-term field exposure. A collaborative effort with U.S. module manufacturers aimed at achieving 30-year module lifetimes is also described
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