450 research outputs found
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
The EBEX Experiment
EBEX is a balloon-borne polarimeter designed to measure the intensity and
polarization of the cosmic microwave background radiation. The measurements
would probe the inflationary epoch that took place shortly after the big bang
and would significantly improve constraints on the values of several
cosmological parameters. EBEX is unique in its broad frequency coverage and in
its ability to provide critical information about the level of polarized
Galactic foregrounds which will be necessary for all future CMB polarization
experiments. EBEX consists of a 1.5 m Dragone-type telescope that provides a
resolution of less than 8 arcminutes over four focal planes each of 4 degree
diffraction limited field of view at frequencies up to 450 GHz. The experiment
is designed to accommodate 330 transition edge bolometric detectors per focal
plane, for a total of up to 1320 detectors. EBEX will operate with frequency
bands centered at 150, 250, 350, and 450 GHz. Polarimetry is achieved with a
rotating achromatic half-wave plate. EBEX is currently in the design and
construction phase, and first light is scheduled for 2008.Comment: 13 pages, 10 figures. Figure 1 is changed from the one which appeared
in the Proceedings of the SPI
MAX 4 and MAX 5 CMB anisotropy measurement constraints on open and flat-Lambda CDM cosmogonies
We account for experimental and observational uncertainties in likelihood
analyses of cosmic microwave background (CMB) anisotropy data from the MAX 4
and MAX 5 experiments. These analyses use CMB anisotropy spectra predicted in
open and spatially-flat Lambda cold dark matter cosmogonies. Amongst the models
considered, the combined MAX data set is most consistent with the CMB
anisotropy shape in Omega_0 ~ 0.1-0.2 open models and less so with that in old
(t_0 >~ 15 - 16 Gyr, i.e., low h), high baryon density (Omega_B >~ 0.0175/h^2),
low density (Omega_0 ~ 0.2 - 0.4), flat-Lambda models. The MAX data alone do
not rule out any of the models we consider at the 2-sigma level.
Model normalizations deduced from the combined MAX data are consistent with
those drawn from the UCSB South Pole 1994 data, except for the flat bandpower
model where MAX favours a higher normalization. The combined MAX data
normalization for open models with Omega_0 ~ 0.1-0.2 is higher than the upper
2-sigma value of the DMR normalization. The combined MAX data normalization for
old (low h), high baryon density, low-density flat-Lambda models is below the
lower 2-sigma value of the DMR normalization. Open models with Omega_0 ~
0.4-0.5 are not far from the shape most favoured by the MAX data, and for these
models the MAX and DMR normalizations overlap. The MAX and DMR normalizations
also overlap for Omega_0 = 1 and some higher h, lower Omega_B, low-density
flat-Lambda models.Comment: Latex, 37 pages, uses aasms4 styl
Supernovae Ia Constraints on a Time-Variable Cosmological "Constant"
The energy density of a scalar field with potential , , behaves like a time-variable cosmological
constant that could contribute significantly to the present energy density.
Predictions of this spatially-flat model are compared to recent Type Ia
supernovae apparent magnitude versus redshift data. A large region of model
parameter space is consistent with current observations. (These constraints are
based on the exact scalar field model equations of motion, not on the widely
used time-independent equation of state fluid approximation equations of
motion.) We examine the consequences of also incorporating constraints from
recent measurements of the Hubble parameter and the age of the universe in the
constant and time-variable cosmological constant models. We also study the
effect of using a non-informative prior for the density parameter.Comment: Accepted for publication in Ap
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
Determining Foreground Contamination in CMB Observations: Diffuse Galactic Emission in the MAXIMA-I Field
Observations of the CMB can be contaminated by diffuse foreground emission
from sources such as Galactic dust and synchrotron radiation. In these cases,
the morphology of the contaminating source is known from observations at
different frequencies, but not its amplitude at the frequency of interest for
the CMB. We develop a technique for accounting for the effects of such emission
in this case, and for simultaneously estimating the foreground amplitude in the
CMB observations. We apply the technique to CMB data from the MAXIMA-1
experiment, using maps of Galactic dust emission from combinations of IRAS and
DIRBE observations, as well as compilations of Galactic synchrotron emission
observations. The spectrum of the dust emission over the 150--450 GHz observed
by MAXIMA is consistent with preferred models but the effect on CMB power
spectrum observations is negligible.Comment: 19 pages, 8 figures, accepted for publication in the Astrophysical
Journal. Monor changes to match the published versio
Estimate of the Cosmological Bispectrum from the MAXIMA-1 Cosmic Microwave Background Map
We use the measurement of the cosmic microwave background taken during the
MAXIMA-1 flight to estimate the bispectrum of cosmological perturbations. We
propose an estimator for the bispectrum that is appropriate in the flat sky
approximation, apply it to the MAXIMA-1 data and evaluate errors using
bootstrap methods. We compare the estimated value with what would be expected
if the sky signal were Gaussian and find that it is indeed consistent, with a
per degree of freedom of approximately unity. This measurement places
constraints on models of inflation.Comment: 5 pages, 2 figures. New version to match paper accepted for
publication in Phys. Rev. Lett. Non-diagonal terms included leading to new
limits on f_N
Dark energy perturbations and cosmic coincidence
While there is plentiful evidence in all fronts of experimental cosmology for
the existence of a non-vanishing dark energy (DE) density \rho_D in the
Universe, we are still far away from having a fundamental understanding of its
ultimate nature and of its current value, not even of the puzzling fact that
\rho_D is so close to the matter energy density \rho_M at the present time
(i.e. the so-called "cosmic coincidence" problem). The resolution of some of
these cosmic conundrums suggests that the DE must have some (mild) dynamical
behavior at the present time. In this paper, we examine some general properties
of the simultaneous set of matter and DE perturbations (\delta\rho_M,
\delta\rho_D) for a multicomponent DE fluid. Next we put these properties to
the test within the context of a non-trivial model of dynamical DE (the LXCDM
model) which has been previously studied in the literature. By requiring that
the coupled system of perturbation equations for \delta\rho_M and \delta\rho_D
has a smooth solution throughout the entire cosmological evolution, that the
matter power spectrum is consistent with the data on structure formation and
that the "coincidence ratio" r=\rho_D/\rho_M stays bounded and not unnaturally
high, we are able to determine a well-defined region of the parameter space
where the model can solve the cosmic coincidence problem in full compatibility
with all known cosmological data.Comment: Typos correcte
Making Maps Of The Cosmic Microwave Background: The MAXIMA Example
This work describes Cosmic Microwave Background (CMB) data analysis
algorithms and their implementations, developed to produce a pixelized map of
the sky and a corresponding pixel-pixel noise correlation matrix from time
ordered data for a CMB mapping experiment. We discuss in turn algorithms for
estimating noise properties from the time ordered data, techniques for
manipulating the time ordered data, and a number of variants of the maximum
likelihood map-making procedure. We pay particular attention to issues
pertinent to real CMB data, and present ways of incorporating them within the
framework of maximum likelihood map-making. Making a map of the sky is shown to
be not only an intermediate step rendering an image of the sky, but also an
important diagnostic stage, when tests for and/or removal of systematic effects
can efficiently be performed. The case under study is the MAXIMA data set.
However, the methods discussed are expected to be applicable to the analysis of
other current and forthcoming CMB experiments.Comment: Replaced to match the published version, only minor change
Multiple Methods for Estimating the Bispectrum of the Cosmic Microwave Background with Application to the MAXIMA Data
We describe different methods for estimating the bispectrum of Cosmic
Microwave Background data. In particular we construct a minimum variance
estimator for the flat-sky limit and compare results with previously-studied
frequentist methods. Application to the MAXIMA dataset shows consistency with
primordial Gaussianity. Weak quadratic non-Gaussianity is characterised by a
tunable parameter , corresponding to non-Gaussianity at a level (ratio of non-Gaussian to Gaussian terms), and we find limits of
for the minimum-variance estimator and for the
usual frequentist estimator. These are the tightest limits on primordial
non-Gaussianity which include the full effects of the radiation transfer
function.Comment: 24 pages, 13 figure
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