48 research outputs found
Cosmological Parameter Estimation: Method
CMB anisotropy data could put powerful constraints on theories of the
evolution of our Universe. Using the observations of the large number of CMB
experiments, many studies have put constraints on cosmological parameters
assuming different frameworks. Assuming for example inflationary paradigm, one
can compute the confidence intervals on the different components of the energy
densities, or the age of the Universe, inferred by the current set of CMB
observations. The aim of this note is to present some of the available methods
to derive the cosmological parameters with their confidence intervals from the
CMB data, as well as some practical issues to investigate large number of
parameters
Photobiomodulation preserves mitochondrial redox state and is retinoprotective in a rodent model of retinitis pigmentosa
Photobiomodulation (PBM) by far-red (FR) to near-infrared (NIR) light has been demonstrated to restore the function of damaged mitochondria, increase the production of cytoprotective factors and prevent cell death. Our laboratory has shown that FR PBM improves functional and structural outcomes in animal models of retinal injury and retinal degenerative disease. The current study tested the hypothesis that a brief course of NIR (830 nm) PBM would preserve mitochondrial metabolic state and attenuate photoreceptor loss in a model of retinitis pigmentosa, the P23H transgenic rat. P23H rat pups were treated with 830 nm light (180 s; 25 mW/cm2; 4.5 J/cm2) using a light-emitting diode array (Quantum Devices, Barneveld, WI) from postnatal day (p) 10 to p25. Sham-treated rats were restrained, but not treated with 830 nm light. Retinal metabolic state, function and morphology were assessed at p30 by measurement of mitochondrial redox (NADH/FAD) state by 3D optical cryo-imaging, electroretinography (ERG), spectral-domain optical coherence tomography (SD-OCT), and histomorphometry. PBM preserved retinal metabolic state, retinal function, and retinal morphology in PBM-treated animals compared to the sham-treated group. PBM protected against the disruption of the oxidation state of the mitochondrial respiratory chain observed in sham-treated animals. Scotopic ERG responses over a range of flash intensities were significantly greater in PBM-treated rats compared to sham controls. SD-OCT studies and histological assessment showed that PBM preserved the structural integrity of the retina. These findings demonstrate for the first time a direct effect of NIR PBM on retinal mitochondrial redox status in a well-established model of retinal disease. They show that chronic proteotoxic stress disrupts retinal bioenergetics resulting in mitochondrial dysfunction, and retinal degeneration and that therapies normalizing mitochondrial metabolism have considerable potential for the treatment of retinal degenerative disease
MAXIPOL: Cosmic Microwave Background Polarimetry Using a Rotating Half-Wave Plate
We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure
the E-mode polarization of the cosmic microwave background radiation (CMB).
MAXIPOL is the first bolometric CMB experiment to observe the sky using rapid
polarization modulation. To build MAXIPOL, the CMB temperature anisotropy
experiment MAXIMA was retrofitted with a rotating half-wave plate and a
stationary analyzer. We describe the instrument, the observations, the
calibration and the reduction of data collected with twelve polarimeters
operating at 140 GHz and with a FWHM beam size of 10 arcmin. We present maps of
the Q and U Stokes parameters of an 8 deg^2 region of the sky near the star
Beta Ursae Minoris. The power spectra computed from these maps give weak
evidence for an EE signal. The maximum-likelihood amplitude of
l(l+1)C^{EE}_{l}/(2 pi) is 55_{-45}^{+51} uK^2 (68%), and the likelihood
function is asymmetric and skewed positive such that with a uniform prior the
probability that the amplitude is positive is 96%. This result is consistent
with the expected concordance LCDM amplitude of 14 uK^2. The maximum likelihood
amplitudes for l(l+1)C^{BB}_{l}/(2 pi) and are
-31_{-19}^{+31} and 18_{-34}^{+27} uK^2 (68%), respectively, which are
consistent with zero. All of the results are for one bin in the range 151 < l <
693. Tests revealed no residual systematic errors in the time or map domain. A
comprehensive discussion of the analysis of the data is presented in a
companion paper.Comment: 19 pages, 11 figures, 2 tables, submitted to Ap
The impact of cluster mergers on arc statistics
We study the impact of merger events on the strong lensing properties of
galaxy clusters. Previous lensing simulations were not able to resolve
dynamical time scales of cluster lenses, which arise on time scales which are
of order a Gyr. In this case study, we first describe qualitatively with an
analytic model how some of the lensing properties of clusters are expected to
change during merging events. We then analyse a numerically simulated lens
model for the variation in its efficiency for producing both tangential and
radial arcs while a massive substructure falls onto the main cluster body. We
find that: (1) during the merger, the shape of the critical lines and caustics
changes substantially; (2) the lensing cross sections for long and thin arcs
can grow by one order of magnitude and reach their maxima when the extent of
the critical curves is largest; (3) the cross section for radial arcs also
grows, but the cluster can efficiently produce this kind of arcs only while the
merging substructure crosses the main cluster centre; (4) while the arc cross
sections pass through their maxima as the merger proceeds, the cluster's X-ray
emission increases by a factor of . Thus, we conclude that accounting
for these dynamical processes is very important for arc statistics studies. In
particular, they may provide a possible explanation for the arc statistics
problem.Comment: 16 pages, submitted to MNRAS, revised version after referee'
Comments. Gzipped file including full resolution images can be downloaded at
http://dipastro.pd.astro.it/~cosmo/massimo/high-res-images.tar.g
Arc Statistics in Cosmological Models with Dark Energy
We investigate how the probability of the formation of giant arcs in galaxy
clusters is expected to change in cosmological models dominated by dark energy
with an equation of state p=w rho c^2 compared to cosmological-constant or open
models. To do so, we use a simple analytic model for arc cross sections based
on the Navarro-Frenk-White density profile which we demonstrate reproduces
essential features of numerically determined arc cross sections. Since analytic
lens models are known to be inadequate for accurate absolute quantifications of
arc probabilities, we use them only for studying changes relative to
cosmological-constant models. Our main results are (1) the order of magnitude
difference between the arc probabilities in low density, spatially flat and
open CDM models found numerically is reproduced by our analytic model, and (2)
dark-energy cosmologies with w>-1 increase the arc optical depth by at most a
factor of two and are thus unlikely to reconcile arc statistics with spatially
flat cosmological models with low matter density.Comment: 8 pages, accepted by A&
Frequentist Estimation of Cosmological Parameters from the MAXIMA-1 Cosmic Microwave Background Anisotropy Data
We use a frequentist statistical approach to set confidence intervals on the
values of cosmological parameters using the MAXIMA-1 and COBE measurements of
the angular power spectrum of the cosmic microwave background. We define a
statistic, simulate the measurements of MAXIMA-1 and COBE,
determine the probability distribution of the statistic, and use it and the
data to set confidence intervals on several cosmological parameters. We compare
the frequentist confidence intervals to Bayesian credible regions. The
frequentist and Bayesian approaches give best estimates for the parameters that
agree within 15%, and confidence interval-widths that agree within 30%. The
results also suggest that a frequentist analysis gives slightly broader
confidence intervals than a Bayesian analysis. The frequentist analysis gives
values of \Omega=0.89{+0.26\atop -0.19}, \Omega_{\rm B}h^2=0.026{+0.020\atop
-0.011} and n=1.02{+0.31\atop -0.10}, and the Bayesian analysis gives values of
\Omega=0.98{+0.14\atop -0.19}, \Omega_{\rm B}h^2=0.0.029{+0.015\atop-0.010},
and , all at the 95% confidence level.Comment: 10 pages, 9 Postscript figures, changes made to reflect published
versio
Acceleration of the universe, vacuum metamorphosis, and the large-time asymptotic form of the heat kernel
We investigate the possibility that the late acceleration observed in the
rate of expansion of the universe is due to vacuum quantum effects arising in
curved spacetime. The theoretical basis of the vacuum cold dark matter (VCDM),
or vacuum metamorphosis, cosmological model of Parker and Raval is revisited
and improved. We show, by means of a manifestly nonperturbative approach, how
the infrared behavior of the propagator (related to the large-time asymptotic
form of the heat kernel) of a free scalar field in curved spacetime causes the
vacuum expectation value of its energy-momentum tensor to exhibit a resonance
effect when the scalar curvature R of the spacetime reaches a particular value
related to the mass of the field. we show that the back reaction caused by this
resonance drives the universe through a transition to an accelerating expansion
phase, very much in the same way as originally proposed by Parker and Raval.
Our analysis includes higher derivatives that were neglected in the earlier
analysis, and takes into account the possible runaway solutions that can follow
from these higher-derivative terms. We find that the runaway solutions do not
occur if the universe was described by the usual classical FRW solution prior
to the growth of vacuum energy-density and negative pressure (i.e., vacuum
metamorphosis) that causes the transition to an accelerating expansion of the
universe in this theory.Comment: 33 pages, 3 figures. Submitted to Physical Review D15 (Dec 23, 2003).
v2: 1 reference added. No other change
The MAXIMA Experiment: Latest Results and Consistency Tests
The MAXIMA cosmic microwave background anisotropy experiment had a
significant impact on cosmology. Results from the program have played a
significant role in determining the geometry of the universe, given strong
supporting evidence to inflation, and, in combination with other astrophysical
data, showed that the universe is filled with dark matter and energy. We
present a subset of the internal consistency checks that were carried out on
the MAXIMA-1 data prior to their release, which demonstrate that systematics
errors were much smaller than statistical errors. We also discuss the MAXIMA-2
flight and data, compare the maps of MAXIMA-1 and -2 in areas where they
overlap and show that the two independent experiments confirm each other. All
of these results demonstrate that MAXIMA mapped the cosmic microwave background
anisotropy with high accuracyComment: to be published in C.R. Physique, 2003, (Academie des Science), 14
pages, figures embedded, a version with high quality figures is available
from http://cosmology.berkeley.edu/maxima/comp_publications.htm
MAXIPOL: a balloon-borne experiment for measuring the polarization anisotropy of the cosmic microwave background radiation
We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure the E-mode polarization anisotropy of the cosmic microwave background radiation (CMB) on angular scales of 10 arcmin to 2 degrees. MAXIPOL is the first CMB experiment to collect data with a polarimeter that utilizes a rotating half-wave plate and fixed wire-grid polarizer. We present the instrument design, elaborate on the polarimeter strategy and show the instrument performance during flight with some time domain data. Our primary data set was collected during a 26 hour turnaround flight that was launched from the National Scientific Ballooning Facility in Ft. Sumner, New Mexico in May 2003. During this flight five regions of the sky were mapped. Data analysis is in progress
Cosmological implications of the MAXIMA-I high resolution Cosmic Microwave Background anisotropy measurement
We discuss the cosmological implications of the new constraints on the power spectrum of the Cosmic Microwave Background Anisotropy derived from a new high resolution analysis of the MAXIMA-1 measurement (Lee et al. 2001). The power spectrum shows excess power at over the average level of power at This excess is statistically significant on the 95% confidence level. Such a feature is consistent with the presence of a third acoustic peak, which is a generic prediction of inflation-based models. The height and the position of the excess power match the predictions of a family of inflationary models with cosmological parameters that are fixed to fit the CMB data previously provided by BOOMERANG-LDB and MAXIMA-1 experiments (e.g., Jaffe et al.2001). Our results, therefore, lend support for inflationary models and more generally for the dominance of coherent perturbations in the structure formation of the Universe. At the same time, they seem to disfavor a large variety of the non-standard (but still inflation-based) models that have been proposed to improve the quality of fits to the CMB data and consistency with other cosmological observables. Within standard inflationary models, our results combined with the COBE-DMR data give best fit values and 95% confidence limits for the baryon density, , and the total density, . The primordial spectrum slope () and the optical depth to the last scattering surface () are found to be degenerate and to obey the relation , for (all 95% c.l.)