1,017 research outputs found
Astrophysical foregrounds and primordial tensor-to-scalar ratio constraints from CMB B-mode polarization observations
We study the effects of astrophysical foregrounds on the ability of CMB
B-mode polarization experiments to constrain the primordial tensor-to-scalar
ratio, r. To clean the foreground contributions we use parametric, maximum
likelihood component separation technique, and consider experimental setups
optimized to render a minimal level of the foreground residuals in the
recovered CMB map. We consider nearly full-sky observations, include two
diffuse foreground components, dust and synchrotron, and study cases with and
without calibration errors, spatial variability of the foreground properties,
and partial or complete B-mode lensing signal removal.
In all these cases we find that in the limit of very low noise level and in
the absence of the intrumental or modeling systematic effects, the foreground
residuals do not lead to a limit on the lowest detectable value of r. But the
need to control the foreground residuals will play a major role in determining
the minimal noise levels necessary to permit a robust detection of r < 0.1 and
therefore in optimizing and forecasting the performance of the future missions.
For current and proposed experiments noise levels, the foreground residuals are
found non-negligible and potentially can affect our ability to set constraints
on r. We also show how the constraints can be significantly improved on by
restricting the post component separation processing to a smaller sky area.
This procedure applied to a case of a COrE-like satellite mission is shown to
result potentially in over an order of magnitude improvement in the detectable
value of r. With sufficient knowledge of the experimental bandpasses as well as
foreground component scaling laws, our conclusions are found to be independent
on the assumed overall normalization of the foregrounds and only quantitatively
depend on specific parametrizations assumed for the foreground components.Comment: 5 pages, 2 figure
Robust forecasts on fundamental physics from the foreground-obscured, gravitationally-lensed CMB polarization
[Abridged] Recent results from the BICEP, Keck Array and Planck
Collaborations demonstrate that Galactic foregrounds are an unavoidable
obstacle in the search for evidence of inflationary gravitational waves in the
cosmic microwave background (CMB) polarization. Beyond the foregrounds, the
effect of lensing by intervening large-scale structure further obscures all but
the strongest inflationary signals permitted by current data. With a plethora
of ongoing and upcoming experiments aiming to measure these signatures, careful
and self-consistent consideration of experiments' foreground- and
lensing-removal capabilities is critical in obtaining credible forecasts of
their performance. We investigate the capabilities of instruments such as
Advanced ACTPol, BICEP3 and Keck Array, CLASS, EBEX10K, PIPER, Simons Array,
SPT-3G and SPIDER, and projects as COrE+, LiteBIRD-ext, PIXIE and Stage IV, to
clean contamination due to polarized synchrotron and dust from raw
multi-frequency data, and remove lensing from the resulting co-added CMB maps
(either using iterative CMB-only techniques or through cross-correlation with
external data). Incorporating these effects, we present forecasts for the
constraining power of these experiments in terms of inflationary physics, the
neutrino sector, and dark energy parameters. Made publicly available through an
online interface, this tool enables the next generation of CMB experiments to
foreground-proof their designs, optimize their frequency coverage to maximize
scientific output, and determine where cross-experimental collaboration would
be most beneficial. We find that analyzing data from ground, balloon and space
instruments in complementary combinations can significantly improve component
separation performance, delensing, and cosmological constraints over individual
datasets.Comment: 37 pages plus appendices, 15 figures; first two authors contributed
equally to this work; forecasting tool available at http://turkey.lbl.gov.
v4: matches version published in JCAP (with extended dark energy constraints
Characterising cosmic birefringence in the presence of galactic foregrounds and instrumental systematic effects
We study a possibility of constraining isotropic cosmic birefringence with
help of cosmic microwave background polarisation data in the presence of
polarisation angle miscalibration without relying on any assumptions about the
Galactic foreground angular power spectra and in particular on their EB
correlation. We propose a new analysis framework based on a generalised
parametric component separation approach, which accounts simultaneously on the
presence of galactic foregrounds, relevant instrumental effects and external
priors. We find that upcoming multi-frequency CMB data with appropriate
calibration priors will allow producing an instrumental-effect-corrected and
foreground-cleaned CMB map, which can be used to estimate the isotropic
birefringence angle and the tensor-to-scalar ratio, accounting on statistical
and systematic uncertainties incurred during the entire procedure. In
particular, in the case of a Simons Observatory-like, three Small Aperture
Telescopes, we derive an uncertainty on the birefringence angle of
(0.1), assuming the standard cosmology
and calibration priors for all (single) frequency channels with the precision
of as aimed at by the near future ground-based
experiments. This implies that these experiments could confirm or disprove the
recently detected value of with a significance between
and . [abridged version]Comment: 20 pages, 9 figure
La chasse aux modes-B du fond diffus cosmologique dans la jungle des contaminations systématiques
This thesis presents a study of selected instrumental and astrophysical systematics, which may affect the performance of new generation of future observations of the Cosmic Microwave Background (CMB) polarization. It elaborates on their impact on the science goals of those observations and discusses techniques and approaches for their removal. Its focus is on general issues typical of entire classes of experiments, but also on specific problems as encountered in the context of a CMB B-mode experiment, POLARBEAR. The main target of the CMB polarization effort undergoing currently in the field is a detection of the primordial B-modes anisotropies --- a so far undetected signature of the inflationary theories. This would have far-reaching impact on our understanding of the universe but also fundamental laws of physics. Understanding, modelling, and ultimately removal of the systematics are essential steps in any modern CMB analysis pipeline and their successful accomplishment, together with a high instrumental sensitivity, will decide of a final success of the entire effort. In this thesis I first describe optics of typical CMB experiments and introduce a parametrization of instrumental and cross-polarization effects particularly convenient for the analysis of their impact. Second, I present a model describing the atmospheric contamination and use it to provide some insights about the atmosphere's role and its impact on performance of ground-based experiments. I also outline how it could be used further to improve control of atmospheric effects in the CMB data analysis. Then, I discuss another source of sky systematics --- the polarized astrophysical foregrounds. In this context I present on the one hand a new approach to forecasting performance of the future experiments, which accounts for the presence of the foregrounds, while on the other I propose a framework for optimizing hardware of such experiments to let them achieve better performance. This part of thesis stems from a common work with drs. F. Stivoli and R. Stompor. I finally present one of the leading CMB polarization experiment POLARBEAR, in which I have been involved in over the course of my PhD studies. I describe its current status and performance as well as selected steps of its data analysis pipeline. In particular, I show methods to estimate some of the parameters introduced for the systematics modeling from simulated data. This work has been performed in collaboration with members of the POLARBEAR team.Cette thèse présente une étude de certains effets systématiques instrumentaux et astrophysiques, pouvant affecter les performances des nouvelles et futures générations d'observations de la polarisation du fond diffus cosmologique (CMB). Nous étudions l'impact de ces effets sur les objectifs scientifiques de ces observations, ainsi que les techniques pour leur élimination. Ce travail se concentre sur les problèmes généraux que rencontrent les expériences de manière générale, mais se penche également sur les questions plus spécifiques soulevées dans le cadre de l'expérience d'observation des modes-B du CMB, POLARBEAR. L'objectif principal de l'effort actuel pour l'étude de la polarisation du CMB est une détection des anisotropies primordiales appelées modes-B --- une signature des théories inflationnaires non détectée à ce jour. Cela aurait un grand impact sur notre compréhension de l'univers, mais aussi des lois fondamentales de la physique. Comprendre, modéliser, et, finalement, éliminer ces effets systématiques sont des éléments indispensables pour tout pipeline d'analyse moderne du CMB. Sa réussite, de concert avec une haute sensibilité instrumentale, décidera du succès final des efforts entrepris. Dans cette thèse je décris tout d'abord l'optique des expériences typiques d'observation du CMB et propose un paramétrage des polarisations instrumentale et croisée. Deuxièmement, je présente un modèle décrivant la contamination atmosphérique et utilise celui-ci afin de donner quelques aperçus sur le rôle et l'impact de l'atmosphère sur les performances des expériences au sol. J'indique également comment ces résultats peuvent être utilisés pour améliorer le contrôle des effets atmosphériques dans l'analyse des données CMB. Ensuite, je discute d'une autre source d'effets systématiques venant du ciel --- les avants-plans astrophysiques polarisés. Dans ce contexte, je présente d'une part une nouvelle approche pour prédire les performances des futures expériences prenant en compte la présence des avant-plans, et d'autre part je propose un cadre pour l'optimisation des expériences afin qu'elles puissent atteindre de meilleures performances. Cette partie de la thèse est issue d'un travail commun avec F. Stivoli et R. Stompor. Je présente enfin une expèrience phare pour l'observation de la polarisation du CMB, POLARBEAR, dans laquelle j'ai été impliqué au cours de mes études doctorales. Je décris le statut actuel et les performances de l'instrument ainsi que quelques étapes de son pipeline d'analyse des données. En particulier, je montre des méthodes d'estimation de certains des paramètres introduits pour la modélisation d'effets systématiques, à partir de données simulées. Ce travail a été réalisé en collaboration avec les membres de l'équipe POLARBEAR
Forecasting performance of CMB experiments in the presence of complex foreground contaminations
We present a new, semianalytic framework for estimating the level of residuals present in cosmic microwave background (CMB) maps derived from multifrequency CMB data and forecasting their impact on cosmological parameters. The data are assumed to contain non-negligible signals of astrophysical and/or Galactic origin, which we clean using a parametric component separation technique. We account for discrepancies between the foreground model assumed during the separation procedure and the true one, allowing for differences in scaling laws and/or their spatial variations. Our estimates and their uncertainties include both systematic and statistical effects and are averaged over the instrumental noise and CMB signal realizations. The framework can be further extended to account self-consistently for existing uncertainties in the foreground models. We demonstrate and validate the framework on simple study cases which aim at estimating the tensor-to-scalar ratio, r. The proposed approach is computationally efficient permitting an investigation of hundreds of setups and foreground models on a single CPU
The origin of the chemical profiles of fungal symbionts and their significance for nestmate recognition in Acromyrmex leaf-cutting ants
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CFD for the Study of the Multiphase Flow and Mass Transfer in a Stirred Tank Reactor for the Screening of Shaped Catalysts
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Detection of relic gravitational waves in the CMB: Prospects for CMBPol mission
Detection of relic gravitational waves, through their imprint in the cosmic
microwave background radiation, is one of the most important tasks for the
planned CMBPol mission. In the simplest viable theoretical models the
gravitational wave background is characterized by two parameters, the
tensor-to-scalar ratio and the tensor spectral index . In this paper,
we analyze the potential joint constraints on these two parameters, and
, using the potential observations of the CMBPol mission, which is
expected to detect the relic gravitational waves if . The
influence of the contaminations, including cosmic weak lensing, various
foreground emissions, and systematical errors, is discussed.Comment: 26 pages, 19 figures, 4 tables; JCAP in pres
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