Statistical isotropy violation in WMAP CMB maps resulting from non-circular beams

Das, Santanu; Mitra, S.; Rotti, Aditya; Pant, Nidhi; Souradeep, T.

doi:10.1051/0004-6361/201424164

Cited by 13 publications

(27 citation statements)

References 33 publications

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“…For a perfectly circular beam profile, B(γ, γ ) ≡ B(γ · γ ), assumed in this work, it is easy to deconvolve the effect of the beam after inferring the power spectra. However, if the beam is not circular symmetric then the effect of the beam depends on the full scan pattern of the experiment and its deconvolution may be non-trivial [3,4,[27][28][29].…”

Section: A Brief Review Of Biposh Representationmentioning

confidence: 99%

“…The biposh representation splits the covariance matrix into pieces that transform separately under the action of the group of rotation SO (3). The scalar (rotationally invariant) term is the power spectrum, C l .…”

Section: A Brief Review Of Biposh Representationmentioning

confidence: 99%

“…Later it was revealed that the signal SI violation signals detected were caused due to the mild non-circularity of the beam response of the WMAP experiment coupled to its particular scan pattern [3]. Therefore as a non-SI case study, we take a SI HEALPix map and scan it with a WMAP-like scan strategy using the publicly available (mildly non-circular symmetric) WMAP W1 band beam response maps to generate a simulated time ordered data stream.…”

Section: Beam Anisotropy Sourced Non-si Mapmentioning

confidence: 99%

“…Bipolar Spherical harmonic representation (BipoSH) was first proposed by Hajian and Souradeep [1] to analyze SI violation signals on CMB. Any SI violation of a random field on a sphere can be completely represented in BipoSH spectra (Ã LM ll ) [2][3][4][5]. The L = 0 component of the BipoSH spectra,Ã 00 ll , is the angular power spectrum, C l .…”

Section: Introductionmentioning

confidence: 99%

“…Artefacts of observational reality such as anisotropic noise, foreground residuals from inadequate cleaning, effect of non-circular beam response function, etc. [2][3][4] may also yield similar SI violation. Therefore, it is necessary to extract the SI violation signal from observational data accounting for any false signal of observational systematics, and then carefully statistically assess its significance vis a vis peculiarity of a particular realisation of SI covariance.…”

Section: Introductionmentioning

confidence: 99%

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Bayesian inference on the sphere beyond statistical isotropy

Das¹,

Wandelt²,

Souradeep³

2015

J. Cosmol. Astropart. Phys.

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Abstract. We present a general method for Bayesian inference of the underlying covariance structure of random fields on a sphere. We employ the Bipolar Spherical Harmonic (BipoSH) representation of general covariance structure on the sphere. We illustrate the efficacy of the method as a principled approach to assess violation of statistical isotropy (SI) in the sky maps of Cosmic Microwave Background (CMB) fluctuations. SI violation in observed CMB maps arise due to known physical effects such as Doppler boost and weak lensing; yet unknown theoretical possibilities like cosmic topology and subtle violations of the cosmological principle, as well as, expected observational artefacts of scanning the sky with a non-circular beam, masking, foreground residuals, anisotropic noise, etc. We explicitly demonstrate the recovery of the input SI violation signals with their full statistics in simulated CMB maps. Our formalism easily adapts to exploring parametric physical models with non-SI covariance, as we illustrate for the inference of the parameters of a Doppler boosted sky map. Our approach promises to provide a robust quantitative evaluation of the evidence for SI violation related anomalies in the CMB sky by estimating the BipoSH spectra along with their complete posterior.arXiv:1509.07137v1 [astro-ph.CO]

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Section: A Brief Review Of Biposh Representationmentioning

confidence: 99%

Section: A Brief Review Of Biposh Representationmentioning

confidence: 99%

Section: Beam Anisotropy Sourced Non-si Mapmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Bayesian inference on the sphere beyond statistical isotropy

Das¹,

Wandelt²,

Souradeep³

2015

J. Cosmol. Astropart. Phys.

Self Cite

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Is the observable Universe consistent with the cosmological principle?

Aluri

Cea

Chingangbam

et al. 2023

Class. Quantum Grav.

106

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The Cosmological Principle (CP) -- the notion that the Universe is spatially isotropic and homogeneous on large scales -- underlies a century of progress in cosmology. It is conventionally formulated through the Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) cosmologies as the spacetime metric, and culminates in the successful and highly predictive $\Lambda$-Cold-Dark-Matter ($\Lambda$CDM) model. Yet, tensions have emerged within the $\Lambda$CDM model, most notably a statistically significant discrepancy in the value of the Hubble constant, $H_0$. Since the notion of cosmic expansion determined by a single parameter is intimately tied to the CP, implications of the $H_0$ tension may extend beyond $\Lambda$CDM to the CP itself. This review surveys current observational hints for deviations from the expectations of the CP, highlighting synergies and disagreements that warrant further study. Setting aside the debate about individual large structures, potential deviations from the CP include variations of cosmological parameters on the sky, discrepancies in the cosmic dipoles, and mysterious alignments in quasar polarizations and galaxy spins. While it is possible that a host of observational systematics are impacting results, it is equally plausible that precision cosmology may have outgrown the FLRW paradigm, an extremely pragmatic but non-fundamental symmetry assumption.

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Effect of noncircularity of experimental beam on CMB parameter estimation

Das

Mitra

Paulson

2015

J. Cosmol. Astropart. Phys.

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Abstract. Measurement of Cosmic Microwave Background (CMB) anisotropies has been playing a lead role in precision cosmology by providing some of the tightest constrains on cosmological models and parameters. However, precision can only be meaningful when all major systematic effects are taken into account. Non-circular beams in CMB experiments can cause large systematic deviation in the angular power spectrum, not only by modifying the measurement at a given multipole, but also introducing coupling between different multipoles through a deterministic bias matrix. Here we add a mechanism for emulating the effect of a full bias matrix to the Planck likelihood code through the parameter estimation code SCoPE. We show that if the angular power spectrum was measured with a non-circular beam, the assumption of circular Gaussian beam or considering only the diagonal part of the bias matrix can lead to huge error in parameter estimation. We demonstrate that, at least for elliptical Gaussian beams, use of scalar beam window functions obtained via Monte Carlo simulations starting from a fiducial spectrum, as implemented in Planck analyses for example, leads to only few percent of sigma deviation of the best-fit parameters. However, we notice more significant differences in the posterior distributions for some of the parameters, which would in turn lead to incorrect errorbars. These differences can be reduced, so that the errorbars match within few percent, by adding an iterative reanalysis step, where the beam window function would be recomputed using the best-fit spectrum estimated in the first step.

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Statistical isotropy violation in WMAP CMB maps resulting from non-circular beams

Cited by 13 publications

References 33 publications

Bayesian inference on the sphere beyond statistical isotropy

Bayesian inference on the sphere beyond statistical isotropy

Is the observable Universe consistent with the cosmological principle?

Effect of noncircularity of experimental beam on CMB parameter estimation

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