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Title: Joint Bayesian analysis of large angular scale CMB temperature anomalies

Abstract

Cosmic microwave background measurements show an agreement with the concordance cosmology model except for a few notable anomalies: Power Suppression, the lack of large scale power in the temperature data compared to what is expected in the concordance model, and Cosmic Hemispherical Asymmetry, a dipolar breakdown of statistical isotropy. An expansion of the CMB covariance in Bipolar Spherical Harmonics naturally parametrizes both these large-scale anomalies, allowing us to perform an exhaustive, fully Bayesian joint analysis of the power spectrum and violations of statistical isotropy up to the dipole level. Our analysis sheds light on the scale dependence of the Cosmic Hemispherical Asymmetry. Assuming a scale-dependent dipole modulation model with a two-parameter power law form, we explore the posterior pdf of amplitude A($l$ = 16) and the power law index α and find the maximum a posteriori values A *(l = 16) = 0.064 ± 0.022 and $$α_*$$ = -0.92 ± 0.22. The maximum a posteriori direction associated with the Cosmic Hemispherical Asymmetry is ($l,b$) = (247.8 o, -19.6 o) in Galactic coordinates, consistent with previous analyses. We evaluate the Bayes factor BSI-DM to compare the Cosmic Hemispherical Asymmetry model with the isotropic model. The data prefer but do not substantially favor the anisotropic model (BSI-DM=0.4). We consider several priors and find that this evidence ratio is robust to prior choice. The large-scale power suppression does not soften when jointly inferring both the isotropic power spectrum and the parameters of the asymmetric model, indicating no evidence that these anomalies are coupled.

Authors:
 [1]; ORCiD logo [2]; ORCiD logo [3];  [4];  [1]
  1. Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune (India)
  2. Institut d'Astrophysique de Paris, Paris (France); Institut Lagrange de Paris, Paris (France); Centre for Computational Astrophysics, Flatiron Institute, New York, NY (United States)
  3. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Univ. of Wisconsin, Madison, WI (United States)
  4. Institut d'Astrophysique de Paris, Paris (France); Institut Lagrange de Paris, Paris (France); Centre for Computational Astrophysics, Flatiron Institute, New York, NY (United States); Univ. of Illinois, Urbana-Champaign, IL (United States). Dept. of Physics and Astronomy
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1542971
Report Number(s):
arXiv:1902.10155; FERMILAB-PUB-19-112
Journal ID: ISSN 1475-7516; 1722283
Grant/Contract Number:  
AC02-07CH11359
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Cosmology and Astroparticle Physics
Additional Journal Information:
Journal Volume: 2019; Journal Issue: 08; Journal ID: ISSN 1475-7516
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS

Citation Formats

Shaikh, Shabbir, Mukherjee, Suvodip, Das, Santanu, Wandelt, Benjamin D., and Souradeep, Tarun. Joint Bayesian analysis of large angular scale CMB temperature anomalies. United States: N. p., 2019. Web. doi:10.1088/1475-7516/2019/08/007.
Shaikh, Shabbir, Mukherjee, Suvodip, Das, Santanu, Wandelt, Benjamin D., & Souradeep, Tarun. Joint Bayesian analysis of large angular scale CMB temperature anomalies. United States. doi:10.1088/1475-7516/2019/08/007.
Shaikh, Shabbir, Mukherjee, Suvodip, Das, Santanu, Wandelt, Benjamin D., and Souradeep, Tarun. Wed . "Joint Bayesian analysis of large angular scale CMB temperature anomalies". United States. doi:10.1088/1475-7516/2019/08/007.
@article{osti_1542971,
title = {Joint Bayesian analysis of large angular scale CMB temperature anomalies},
author = {Shaikh, Shabbir and Mukherjee, Suvodip and Das, Santanu and Wandelt, Benjamin D. and Souradeep, Tarun},
abstractNote = {Cosmic microwave background measurements show an agreement with the concordance cosmology model except for a few notable anomalies: Power Suppression, the lack of large scale power in the temperature data compared to what is expected in the concordance model, and Cosmic Hemispherical Asymmetry, a dipolar breakdown of statistical isotropy. An expansion of the CMB covariance in Bipolar Spherical Harmonics naturally parametrizes both these large-scale anomalies, allowing us to perform an exhaustive, fully Bayesian joint analysis of the power spectrum and violations of statistical isotropy up to the dipole level. Our analysis sheds light on the scale dependence of the Cosmic Hemispherical Asymmetry. Assuming a scale-dependent dipole modulation model with a two-parameter power law form, we explore the posterior pdf of amplitude A($l$ = 16) and the power law index α and find the maximum a posteriori values A*(l = 16) = 0.064 ± 0.022 and $α_*$ = -0.92 ± 0.22. The maximum a posteriori direction associated with the Cosmic Hemispherical Asymmetry is ($l,b$) = (247.8o, -19.6o) in Galactic coordinates, consistent with previous analyses. We evaluate the Bayes factor BSI-DM to compare the Cosmic Hemispherical Asymmetry model with the isotropic model. The data prefer but do not substantially favor the anisotropic model (BSI-DM=0.4). We consider several priors and find that this evidence ratio is robust to prior choice. The large-scale power suppression does not soften when jointly inferring both the isotropic power spectrum and the parameters of the asymmetric model, indicating no evidence that these anomalies are coupled.},
doi = {10.1088/1475-7516/2019/08/007},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 08,
volume = 2019,
place = {United States},
year = {2019},
month = {8}
}

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