1,991 research outputs found
Evidence for non-Gaussianity in the COBE DMR Four Year Sky Maps
We introduce and study the distribution of an estimator for the normalized
bispectrum of the Cosmic Microwave Background (CMB) anisotropy. We use it to
construct a goodness of fit statistic to test the coadded 53 and 90 GHz
COBE-DMR 4 year maps for non-Gaussianity. Our results indicate that Gaussianity
is ruled out at the confidence level in excess of 98%. This value is a lower
bound, given all the investigated systematics. The dominant non-Gaussian
contribution is found near the multipole of order . Our attempts to
explain this effect as caused by the diffuse foreground emission from the
Galaxy have failed. We conclude that unless there exists a microwave foreground
emission which spatially correlates neither with the DIRBE nor Haslam maps, the
cosmological CMB anisotropy is genuinely non-Gaussian.Comment: 16 pages, 3 figs uses aasms4.tex, revised and accepted to Ap. J. Let
Messengers from the Early Universe: Cosmic Neutrinos and Other Light Relics
The hot dense environment of the early universe is known to have produced large numbers of baryons, photons, and neutrinos. These extreme conditions may have also produced other long-lived species, including new light particles (such as axions or sterile neutrinos) or gravitational waves. The gravitational effects of any such light relics can be observed through their unique imprint in the cosmic microwave background (CMB), the large-scale structure, and the primordial light element abundances, and are important in determining the initial conditions of the universe. We argue that future cosmological observations, in particular improved maps of the CMB on small angular scales, can be orders of magnitude more sensitive for probing the thermal history of the early universe than current experiments. These observations offer a unique and broad discovery space for new physics in the dark sector and beyond, even when its effects would not be visible in terrestrial experiments or in astrophysical environments. A detection of an excess light relic abundance would be a clear indication of new physics and would provide the first direct information about the universe between the times of reheating and neutrino decoupling one second later
Fast CMB Power Spectrum Estimation of Temperature and Polarisation with Gabor Transforms
We extend the analysis of Gabor transforms on a Cosmic Microwave Background
(CMB) temperature map (Hansen, Gorski and Hivon 2002) to polarisation. We study
the temperature and polarisation power spectra on the cut sky, the so-called
pseudo power spectra. The transformation kernels relating the full-sky
polarisation power spectra and the polarisation pseudo power spectra are found
to be similar to the kernel for the temperature power spectrum. This fact is
used to construct a fast power spectrum estimation algorithm using the pseudo
power spectrum of temperature and polarisation as data vectors in a maximum
likelihood approach. Using the pseudo power spectra as input to the likelihood
analysis solves the problem of having to invert huge matrices which makes the
standard likelihood approach infeasible.Comment: 32 pages, 25 figures, submitted to MNRA
Messengers from the Early Universe: Cosmic Neutrinos and Other Light Relics
The hot dense environment of the early universe is known to have produced large numbers of baryons, photons, and neutrinos. These extreme conditions may have also produced other long-lived species, including new light particles (such as axions or sterile neutrinos) or gravitational waves. The gravitational effects of any such light relics can be observed through their unique imprint in the cosmic microwave background (CMB), the large-scale structure, and the primordial light element abundances, and are important in determining the initial conditions of the universe. We argue that future cosmological observations, in particular improved maps of the CMB on small angular scales, can be orders of magnitude more sensitive for probing the thermal history of the early universe than current experiments. These observations offer a unique and broad discovery space for new physics in the dark sector and beyond, even when its effects would not be visible in terrestrial experiments or in astrophysical environments. A detection of an excess light relic abundance would be a clear indication of new physics and would provide the first direct information about the universe between the times of reheating and neutrino decoupling one second later
CMB Anisotropy Constraints on Flat-Lambda and Open CDM Cosmogonies from DMR, UCSB South Pole, Python, ARGO, MAX, White Dish, OVRO, and SuZIE Data
We use joint likelihood analyses of combinations of fifteen cosmic microwave
background (CMB) anisotropy data sets from the DMR, UCSB South Pole 1994,
Python I--III, ARGO, MAX 4 and 5, White Dish, OVRO, and SuZIE experiments to
constrain cosmogonies. We consider open and spatially-flat-Lambda cold dark
matter cosmogonies, with nonrelativistic-mass density parameter Omega_0 in the
range 0.1--1, baryonic-mass density parameter Omega_B in the range
(0.005--0.029) h^{-2}, and age of the universe t_0 in the range (10--20) Gyr.
Marginalizing over all parameters but Omega_0, the data favor Omega_0 \simeq
0.9--1 (0.4--0.6) flat-Lambda (open) models. The range in deduced Omega_0
values is partially a consequence of the different combinations of
smaller-angular-scale CMB anisotropy data sets used in the analyses, but more
significantly a consequence of whether the DMR quadrupole moment is accounted
for or ignored in the analysis. For both flat-Lambda and open models, after
marginalizing over all other parameters, a lower Omega_B h^2 \simeq
0.005--0.009 is favored. This is also marginally at odds with estimates from
more recent CMB anisotropy data and some estimates from standard
nucleosynthesis theory and observed light element abundances. For both sets of
models a younger universe with t_0 \simeq 12--15 Gyr is favored, consistent
with other recent non-CMB indicators. We emphasize that since we consider only
a small number of data sets, these results are tentative. More importantly, the
analyses here do not rule out the currently favored flat-Lambda model with
Omega_0 \sim 0.3, nor the larger Omega_B h^2 values favored by some other data.Comment: 25 pages, 10 figures, submitted to ApJ; the abstract here is slightly
abridge
Cosmic microwave background anisotropy power spectrum statistics for high precision cosmology
As the era of high precision cosmology approaches, the empirically determined
power spectrum of the microwave background anisotropy, , will provide a
crucial test for cosmological theories. We present a unified semi-analytic
framework for the study of the statistical properties of the coefficients
computed from the results of balloon, ground based, and satellite experiments.
An illustrative application shows that commonly used approximations {\it bias}
the estimation of the baryon parameter at the 1% level even for a
satellite capturing as much as % of the sky.Comment: 4 pages, 3 figures. Also available at
http://www.tac.dk/~wandelt/downloads.htm
The primordial non-Gaussianity of local type (f^(local)_(NL)) in the WMAP 5-year data: the length distribution of CMB skeleton
We present skeleton studies of non-Gaussianity in the cosmic microwave background temperature anisotropy observed in the 5-yr Wilkinson Microwave Anisotropy Probe (WMAP) data. The local skeleton is traced on the 2D sphere by cubic spline interpolation which leads to more accurate estimation of the intersection positions between the skeleton and the secondary pixels than conventional linear interpolation. We demonstrate that the skeleton-based estimator of non-Gaussianity of the local type (f^(local)_(NL)) – the departure of the length distribution from the corresponding Gaussian expectation – yields an unbiased and sufficiently converged likelihood function for f^(local)_(NL).
We analyse the skeleton statistics in the WMAP 5-yr combined V- and W-band data outside the Galactic base-mask determined from the KQ75 sky coverage. The results are consistent with Gaussian simulations of the best-fitting cosmological model, but deviate from the previous results determined using the WMAP 1-yr data. We show that it is unlikely that the improved skeleton tracing method, the omission of Q-band data, the modification of the foreground-template fitting method or the absence of six extended regions in the new mask contribute to such a deviation. However, the application of the Kp0 base-mask in data processing does improve the consistency with the WMAP1 results.
The f^(local)_(NL)-likelihood functions of the data are estimated at nine different smoothing levels. It is unexpected that the best-fitting values show positive correlation with the smoothing scales. Further investigation argues against a point source or goodness-of-fit explanation but finds that about 30 per cent of either Gaussian or f_(NL) samples having better goodness-of-fit than the WMAP 5-yr data show a similar correlation. We present the estimate f^(local)_(NL)= 47.3 ± 34.9 (1σ error) determined from the first four smoothing angles and f^(local)_(NL)= 76.8 ± 43.1 for the combination of all nine. The former result may be overestimated at the 0.21σ level because of point sources
Needatool: A Needlet Analysis Tool for Cosmological Data Processing
We introduce NeedATool (Needlet Analysis Tool), a software for data analysis
based on needlets, a wavelet rendition which is powerful for the analysis of
fields defined on a sphere. Needlets have been applied successfully to the
treatment of astrophysical and cosmological observations, and in particular to
the analysis of cosmic microwave background (CMB) data. Usually, such analyses
are performed in real space as well as in its dual domain, the harmonic one.
Both spaces have advantages and disadvantages: for example, in pixel space it
is easier to deal with partial sky coverage and experimental noise; in harmonic
domain, beam treatment and comparison with theoretical predictions are more
effective. During the last decade, however, wavelets have emerged as a useful
tool for CMB data analysis, since they allow to combine most of the advantages
of the two spaces, one of the main reasons being their sharp localisation. In
this paper, we outline the analytical properties of needlets and discuss the
main features of the numerical code, which should be a valuable addition to the
CMB analyst's toolbox.Comment: software available at:
http://www.fisica.uniroma2.it/~pietrobon/dp_files/dp_NeedATool_download.htm
All-sky convolution for polarimetry experiments
We discuss all-sky convolution of the instrument beam with the sky signal in
polarimetry experiments, such as the Planck mission which will map the
temperature anisotropy and polarization of the cosmic microwave background
(CMB). To account properly for stray light (from e.g. the galaxy, sun, and
planets) in the far side-lobes of such an experiment, it is necessary to
perform the beam convolution over the full sky. We discuss this process in
multipole space for an arbitrary beam response, fully including the effects of
beam asymmetry and cross-polarization. The form of the convolution in multipole
space is such that the Wandelt-Gorski fast technique for all-sky convolution of
scalar signals (e.g. temperature) can be applied with little modification. We
further show that for the special case of a pure co-polarized, axisymmetric
beam the effect of the convolution can be described by spin-weighted window
functions. In the limits of a small angle beam and large Legendre multipoles,
the spin-weight 2 window function for the linear polarization reduces to the
usual scalar window function used in previous analyses of beam effects in CMB
polarimetry experiments. While we focus on the example of polarimetry
experiments in the context of CMB studies, we emphasise that the formalism we
develop is applicable to anisotropic filtering of arbitrary tensor fields on
the sphere.Comment: 8 pages, 1 figure; Minor changes to match version accepted by Phys.
Rev.
The primordial non-Gaussianity of local type (f_NL) in the WMAP 5-year data: the length distribution of CMB skeleton
We present skeleton studies of non-Gaussianity in the CMB temperature
anisotropy observed in the WMAP5 data. The local skeleton is traced on the 2D
sphere by cubic spline interpolation which leads to more accurate estimation of
the intersection positions between the skeleton and the secondary pixels than
conventional linear interpolation. We demonstrate that the skeleton-based
estimator of non-Gaussianity of the local type (f_NL) - the departure of the
length distribution from the corresponding Gaussian expectation - yields an
unbiased and sufficiently converged f_NL-likelihood.
We analyse the skeleton statistics in the WMAP5 combined V- and W-band data
outside the Galactic base-mask determined from the KQ75 sky-coverage. The
results are consistent with Gaussian simulations of the the best-fitting
cosmological model, but deviate from the previous results determined using the
WMAP1 data. We show that it is unlikely that the improved skeleton tracing
method, the omission of Q-band data, the modification of the
foreground-template fitting method or the absence of 6 extended regions in the
new mask contribute to such a deviation. However, the application of the Kp0
base-mask in data processing does improve the consistency with the WMAP1
results.
The f_NL-likelihoods of the data are estimated at 9 different smoothing
levels. It is unexpected that the best-fit values show positive correlation
with the smoothing scales. Further investigation argues against a point-source
or goodness-of-fit explanation but finds that about 30% of either Gaussian or
f_NL samples having better goodness-of-fit than the WMAP5 show a similar
correlation. We present the estimate f_NL=47.3+/-34.9 (1sigma error) determined
from the first four smoothing angles and f_NL=76.8+/-43.1 for the combination
of all nine. The former result may be overestimated at the 0.21sigma-level
because of point sources.Comment: 17 pages, 14 figures, 5 tables, accepted for publication in MNRA
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