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Probing the early Universe with B-mode polarization: The Spider instrument, optical modelling and non-Gaussianity
Stockholm University, Faculty of Science, Department of Physics.ORCID iD: 0000-0003-2856-2382
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the main goals of modern observational cosmology is to constrain or detect a stochastic background of primordial gravitational waves. The existence of such a background is a generic prediction of the inflationary paradigm: the leading explanation for the universe's initial perturbations. A detection of the gravitational wave signal would provide strong evidence for the paradigm and would amount to an indirect probe of an energy scale far beyond that of conventional physics. Several dedicated experiments search for the signal by performing highly accurate measurements of a unique probe of the primordial gravitational wave background: the B-mode signature in the polarization of the cosmic microwave background (CMB) radiation. A part of this thesis is devoted to one of these experiments: the balloon-borne Spider instrument. The analysis of the first dataset, obtained in two (95 and 150 GHz) frequency bands during a January 2015 Antarctic flight, is described, along with details on the characterisation of systematic signal and the calibration of the instrument. The case of systematic signal due to poorly understood optical properties is treated in more detail. In the context of upcoming experiments, a study of systematic optical effects is presented as well as a numerically efficient method to consistently propagate such effects through an analysis pipeline. This is achieved by a `beam convolution' algorithm capable of simulating the contribution from the entire sky, weighted by the optical response, to the instrument's time-ordered data. It is described how the algorithm can be employed to forecast the performance of upcoming CMB experiments. In the final part of the thesis, an additional use of upcoming B-mode data is described. Constraints on the non-Gaussian correlation between the large-angular-scale B-mode field and the CMB temperature or E-mode anisotropies on small angular scales constitute a rigorous consistency check of the inflationary paradigm. An efficient statistical estimation procedure, a generalised bispectrum estimator, is derived and the constraining power of upcoming CMB data is explored.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2019.
Keywords [en]
cosmic microwave background, early universe, polarimetry, telescopes
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-171284ISBN: 978-91-7797-799-5 (print)ISBN: 978-91-7797-800-8 (electronic)OAI: oai:DiVA.org:su-171284DiVA, id: diva2:1342131
Public defence
2019-09-20, sal FD41, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 1: Manuscript.

Available from: 2019-08-28 Created: 2019-08-12 Last updated: 2019-08-20Bibliographically approved
List of papers
1. CMB B-mode non-Gaussianity I: Optimal bispectrum estimator and Fisher Forecasts
Open this publication in new window or tab >>CMB B-mode non-Gaussianity I: Optimal bispectrum estimator and Fisher Forecasts
(English)Manuscript (preprint) (Other academic)
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-171283 (URN)
Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-19Bibliographically approved
2. Full-sky beam convolution for cosmic microwave background applications
Open this publication in new window or tab >>Full-sky beam convolution for cosmic microwave background applications
2019 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 486, no 4, p. 5448-5467Article in journal (Refereed) Published
Abstract [en]

We introduce a publicly available full-sky beam convolution code library intended to inform the design of future cosmic microwave background instruments and help current experiments probe potential systematic effects. The code can be used to assess the impact of optical systematics on all stages of data reduction for a realistic experiment, including analyses beyond power spectrum estimation, by generating signal timelines that may serve as input to full analysis pipelines. The design and mathematical framework of the PYTHON code is discussed along with a few simple benchmarking results. We present a simple two-lens refracting telescope design and use it together with the code to simulate a year-long data set for 400 detectors scanning the sky on a satellite instrument. The simulation results identify a number of sub-leading optical non-idealities and demonstrate significant B-mode residuals caused by extended sidelobes that are sensitive to polarized radiation from the Galaxy. For the proposed design and satellite scanning strategy, we show that a full physical optics beam model generates B-mode systematics that differ significantly from the simpler elliptical Gaussian model.

Keywords
Cosmic Background Radiation, Cosmology: observations, Techniques: polarimetric, Telescopes
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-171281 (URN)10.1093/mnras/stz1143 (DOI)000474908200074 ()
Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-19Bibliographically approved
3. The Simons Observatory: science goals and forecasts
Open this publication in new window or tab >>The Simons Observatory: science goals and forecasts
Show others...
2019 (English)In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 2, article id 056Article in journal (Refereed) Published
Abstract [en]

The Simons Observatory (SO) is a new cosmic microwave background experiment being built on Cerro Toco in Chile, due to begin observations in the early 2020s. We describe the scientific goals of the experiment, motivate the design, and forecast its performance. SO will measure the temperature and polarization anisotropy of the cosmic microwave background in six frequency bands centered at: 27, 39, 93, 145, 225 and 280 GHz. The initial con figuration of SO will have three small-aperture 0.5-m telescopes and one large-aperture 6-m telescope, with a total of 60,000 cryogenic bolometers. Our key science goals are to characterize the primordial perturbations, measure the number of relativistic species and the mass of neutrinos, test for deviations from a cosmological constant, improve our understanding of galaxy evolution, and constrain the duration of reionization. The small aperture telescopes will target the largest angular scales observable from Chile, mapping approximate to 10% of the sky to a white noise level of 2 mu K-arcmin in combined 93 and 145 GHz bands, to measure the primordial tensor-to-scalar ratio, r, at a target level of sigma(r) = 0.003. The large aperture telescope will map approximate to 40% of the sky at arcminute angular resolution to an expected white noise level of 6 mu K-arcmin in combined 93 and 145 GHz bands, overlapping with the majority of the Large Synoptic Survey Telescope sky region and partially with the Dark Energy Spectroscopic Instrument. With up to an order of magnitude lower polarization noise than maps from the Planck satellite, the high-resolution sky maps will constrain cosmological parameters derived from the damping tail, gravitational lensing of the microwave background, the primordial bispectrum, and the thermal and kinematic Sunyaev-Zel'dovich effects, and will aid in delensing the large-angle polarization signal to measure the tensor-to-scalar ratio. The survey will also provide a legacy catalog of 16,000 galaxy clusters and more than 20,000 extragalactic sources.

Keywords
CMBR experiments, CMBR polarisation, cosmological parameters from CMBR
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-167547 (URN)10.1088/1475-7516/2019/02/056 (DOI)000459991200002 ()
Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-08-19Bibliographically approved
4. A New Limit on CMB Circular Polarization from SPIDER
Open this publication in new window or tab >>A New Limit on CMB Circular Polarization from SPIDER
Show others...
2017 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 844, no 2, article id 151Article in journal (Refereed) Published
Abstract [en]

We present a new upper limit on cosmic microwave background (CMB) circular polarization from the 2015 flight of SPIDER, a balloon-borne telescope designed to search for B-mode linear polarization from cosmic inflation. Although the level of circular polarization in the CMB is predicted to be very small, experimental limits provide a valuable test of the underlying models. By exploiting the nonzero circular-to-linear polarization coupling of the half-wave plate polarization modulators, data from SPIDER's 2015 Antarctic flight provide a constraint on Stokes V at 95 and 150 GHz in the range 33 < l < 307. No other limits exist over this full range of angular scales, and SPIDER improves on the previous limit by several orders of magnitude, providing 95% C.L. constraints on l (l + 1)C-l(VV) /(2 pi) ranging from 141 to 255 mu K-2 at 150 GHz for a thermal CMB spectrum. As linear CMB polarization experiments become increasingly sensitive, the techniques described in this paper can be applied to obtain even stronger constraints on circular polarization.

Keywords
cosmic background radiation
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-145843 (URN)10.3847/1538-4357/aa7cfd (DOI)000406841700004 ()
Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2019-08-19Bibliographically approved

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