100 research outputs found
General CMB and Primordial Bispectrum Estimation I: Mode Expansion, Map-Making and Measures of f_NL
We present a detailed implementation of two bispectrum estimation methods
which can be applied to general non-separable primordial and CMB bispectra. The
method exploits bispectrum mode decompositions on the domain of allowed
wavenumber or multipole values. Concrete mode examples constructed from
symmetrised tetrahedral polynomials are given, demonstrating rapid convergence
for known bispectra. We use these modes to generate simulated CMB maps of high
resolution (l > 2000) given an arbitrary primordial power spectrum and
bispectrum or an arbitrary late-time CMB angular power spectrum and bispectrum.
By extracting coefficients for the same separable basis functions from an
observational map, we are able to present an efficient and general f_NL
estimator for a given theoretical model. The estimator has two versions
comparing theoretical and observed coefficients at either primordial or late
times, thus encompassing a wider range of models, including secondary
anisotropies, lensing and cosmic strings. We provide examples and validation of
both f_NL estimation methods by direct comparison with simulations in a
WMAP-realistic context. In addition, we show how the full bispectrum can be
extracted from observational maps using these mode expansions, irrespective of
the theoretical model under study. We also propose a universal definition of
the bispectrum parameter F_NL for more consistent comparison between
theoretical models. We obtain WMAP5 estimates of f_NL for the equilateral model
from both our primordial and late-time estimators which are consistent with
each other, as well as with results already published in the literature. These
general bispectrum estimation methods should prove useful for the analysis of
nonGaussianity in the Planck satellite data, as well as in other contexts.Comment: 41 pages, 17 figure
Primordial non-Gaussianity and Bispectrum Measurements in the Cosmic Microwave Background and Large-Scale Structure
The most direct probe of non-Gaussian initial conditions has come from
bispectrum measurements of temperature fluctuations in the Cosmic Microwave
Background and of the matter and galaxy distribution at large scales. Such
bispectrum estimators are expected to continue to provide the best constraints
on the non-Gaussian parameters in future observations. We review and compare
the theoretical and observational problems, current results and future
prospects for the detection of a non-vanishing primordial component in the
bispectrum of the Cosmic Microwave Background and large-scale structure, and
the relation to specific predictions from different inflationary models.Comment: 82 pages, 23 figures; Invited Review for the special issue "Testing
the Gaussianity and Statistical Isotropy of the Universe" for Advances in
Astronom
Combining power spectrum and bispectrum measurements to detect oscillatory features
The simplest inflationary models present us with few observable parameters to
discriminate between them. A detection of features in the spectra of primordial
density perturbations could provide valuable insights and lead to stringent
tests of models of the early Universe. So far, searches for oscillatory
features have not produced statistically significant results. In this work we
consider a combined search for features in the power spectrum and bispectrum.
We show that possible dependencies between the estimates of feature model
amplitudes based on the two- and three-point correlators are largely
statistically independent under the assumption of the null hypothesis of a
nearly Gaussian featureless CMB. Building on this conclusion we propose an
optimal amplitude estimator for a combined search and study the look-elsewhere
effect in feature model surveys. In particular we construct analytic models for
the distribution of amplitude estimates that allow for a reliable assessment of
the significance of potential findings. We also propose a well-behaved
integrated statistic that is designed to detect evidence for models exhibiting
features at multiple frequencies.Comment: v1: 20 pages, 14 figures; v2: references added, typos corrected,
minor changes in introduction; v3: minor changes to match the published
versio
Oscillations in the bispectrum
There exist several models of inflation that produce primordial bispectra
that contain a large number of oscillations. In this paper we discuss these
models, and aim at finding a method of detecting such bispectra in the data. We
explain how the recently proposed method of mode expansion of bispectra might
be able to reconstruct these spectra from separable basis functions. Extracting
these basis functions from the data might then lead to observational
constraints on these models.Comment: 6 pages, 2 figures, submitted to JOP: Conference Series, PASCOS 201
COrE (Cosmic Origins Explorer) A White Paper
COrE (Cosmic Origins Explorer) is a fourth-generation full-sky,
microwave-band satellite recently proposed to ESA within Cosmic Vision
2015-2025. COrE will provide maps of the microwave sky in polarization and
temperature in 15 frequency bands, ranging from 45 GHz to 795 GHz, with an
angular resolution ranging from 23 arcmin (45 GHz) and 1.3 arcmin (795 GHz) and
sensitivities roughly 10 to 30 times better than PLANCK (depending on the
frequency channel). The COrE mission will lead to breakthrough science in a
wide range of areas, ranging from primordial cosmology to galactic and
extragalactic science. COrE is designed to detect the primordial gravitational
waves generated during the epoch of cosmic inflation at more than
for . It will also measure the CMB gravitational lensing
deflection power spectrum to the cosmic variance limit on all linear scales,
allowing us to probe absolute neutrino masses better than laboratory
experiments and down to plausible values suggested by the neutrino oscillation
data. COrE will also search for primordial non-Gaussianity with significant
improvements over Planck in its ability to constrain the shape (and amplitude)
of non-Gaussianity. In the areas of galactic and extragalactic science, in its
highest frequency channels COrE will provide maps of the galactic polarized
dust emission allowing us to map the galactic magnetic field in areas of
diffuse emission not otherwise accessible to probe the initial conditions for
star formation. COrE will also map the galactic synchrotron emission thirty
times better than PLANCK. This White Paper reviews the COrE science program,
our simulations on foreground subtraction, and the proposed instrumental
configuration.Comment: 90 pages Latex 15 figures (revised 28 April 2011, references added,
minor errors corrected
Planck 2015 results. XXVII. The Second Planck Catalogue of Sunyaev-Zeldovich Sources
We present the all-sky Planck catalogue of Sunyaev-Zeldovich (SZ) sources detected from the 29 month full-mission data. The catalogue (PSZ2) is the largest SZ-selected sample of galaxy clusters yet produced and the deepest all-sky catalogue of galaxy clusters. It contains 1653 detections, of which 1203 are confirmed clusters with identified counterparts in external data-sets, and is the first SZ-selected cluster survey containing > confirmed clusters. We present a detailed analysis of the survey selection function in terms of its completeness and statistical reliability, placing a lower limit of 83% on the purity. Using simulations, we find that the Y5R500 estimates are robust to pressure-profile variation and beam systematics, but accurate conversion to Y500 requires. the use of prior information on the cluster extent. We describe the multi-wavelength search for counterparts in ancillary data, which makes use of radio, microwave, infra-red, optical and X-ray data-sets, and which places emphasis on the robustness of the counterpart match. We discuss the physical properties of the new sample and identify a population of low-redshift X-ray under- luminous clusters revealed by SZ selection. These objects appear in optical and SZ surveys with consistent properties for their mass, but are almost absent from ROSAT X-ray selected samples
Generation and Characterization of Large Non-Gaussianities in Single Field Inflation
Inflation driven by a single, minimally coupled, slowly rolling field
generically yields a negligible primordial non-Gaussianity. We discuss two
distinct mechanisms by which a non-trivial potential can generate large
non-Gaussianities. Firstly, if the inflaton traverses a feature in the
potential, or if the inflationary phase is short enough so that initial
transient contributions to the background dynamics have not been erased, modes
near horizon-crossing can acquire significant non-Gaussianities. Secondly,
potentials with small-scale structure may induce significant non-Gaussianities
while the relevant modes are deep inside the horizon. The first case includes
the "step" potential we previously analyzed while the second "resonance" case
is novel. We derive analytic approximations for the 3-point terms generated by
both mechanisms written as products of functions of the three individual
momenta, permitting the use of efficient analysis algorithms. Finally, we
present a significantly improved approach to regularizing and numerically
evaluating the integrals that contribute to the 3-point function.Comment: 29 pp, 8 fig
Exploring cosmic origins with CORE : Inflation
We forecast the scientific capabilities to improve our understanding of cosmic inflation of CORE, a proposed CMB space satellite submitted in response to the ESA fifth call for a medium-size mission opportunity. The CORE satellite will map the CMB anisotropies in temperature and polarization in 19 frequency channels spanning the range 60-600 GHz. CORE will have an aggregate noise sensitivity of 1.7 mu K.arcmin and an angular resolution of 5' at 200 GHz. We explore the impact of telescope size and noise sensitivity on the inflation science return by making forecasts for several instrumental configurations. This study assumes that the lower and higher frequency channels suffice to remove foreground contaminations and complements other related studies of component separation and systematic effects, which will be reported in other papers of the series "Exploring Cosmic Origins with CORE." We forecast the capability to determine key inflationary parameters, to lower the detection limit for the tensor-to-scalar ratio down to the 10(-3) level, to chart the landscape of single field slow-roll inflationary models, to constrain the epoch of reheating, thus connecting inflation to the standard radiation-matter dominated Big Bang era, to reconstruct the primordial power spectrum, to constrain the contribution from isocurvature perturbations to the 10(-3) level, to improve constraints on the cosmic string tension to a level below the presumptive GUT scale, and to improve the current measurements of primordial non-Gaussianities down to the f(NL)(local) <1 level. For all the models explored, CORE alone will improve significantly on the present constraints on the physics of inflation. Its capabilities will be further enhanced by combining with complementary future cosmological observations.Peer reviewe
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