Covariance of CMB anomalies

Muir, J.; Adhikari, Saroj; Huterer, Dragan

doi:10.1103/physrevd.98.023521

Cited by 44 publications

(56 citation statements)

References 68 publications

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“…An existing body of literature also explores connections between different anomalies. For example, Muir et al (2018) [18] investigate the covariance between various anomalies. Polastri et al (2015) [19] study the connection between directional anomaly of low multipole alignment and dipole modulation.…”

Section: Introductionmentioning

confidence: 99%

Joint Bayesian analysis of large angular scale CMB temperature anomalies

Shaikh

Mukherjee

Das

et al. 2019

J. Cosmol. Astropart. Phys.

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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 B SI−DM to compare the Cosmic Hemispherical Asymmetry model with the isotropic model. The data prefer but do not substantially favor the anisotropic model (B SI−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.

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Section: Introductionmentioning

confidence: 99%

Joint Bayesian analysis of large angular scale CMB temperature anomalies

Shaikh

Mukherjee

Das

et al. 2019

J. Cosmol. Astropart. Phys.

View full text Add to dashboard Cite

show abstract

“…After these four new parameters we include the best-fit values of the four standard parameters: the dimensionless rescaled Hubble scale h, the spectral index n s and amplitude A s of the fiducial PPS (1), and finally the reionization optical depth τ (which is computed as a derived quantity from the best-fit values). To complete the tables we add the LRT statistics Γ defined by (16) and (in the last column) the p−value γ defined by (18). To the last column we add (in round brackets) the probability γ translated into the corresponding number of one-dimensional Gaussian standard deviations, and also (in square brackets) the number of extra degrees of freedom.…”

Section: A General Considerationsmentioning

confidence: 99%

“…Besides the low power at large angular scales, other so-called anomalies have also been considered (see for example Ref. [18] for a summary of these anomalies and tests of their statistical significance). While statistical analysis of "anomalies" can shed light on their significance, these a posteriori methods tend to overestimate the significance 1 .…”

Section: Introductionmentioning

confidence: 99%

Modeling the large-scale power deficit with smooth and discontinuous primordial spectra

2019

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We study primordial power spectra with a large-scale power deficit and their effect on the standard ΛCDM cosmology. The standard power-law spectrum is subject to long-wavelength modifications described by some new parameters, resulting in corrections to the anisotropies in the cosmic microwave background. The new parameters are fitted to different datasets: Planck 2015 data for temperature and for both temperature and polarization, the low-redshift determination of H0, and distances derived from baryonic acoustic oscillations. We discuss the statistical significance of the modified spectra, from both frequentist and Bayesian perspectives. Our analysis suggests motivations for considering models that break scalar-tensor consistency, or models with negligible power in the far super-Hubble limit. We present what appears to be substantial evidence, according to the Jeffreys' scale, for a new length scale around 2200 Mpc (k −1 ∼ 350 Mpc) above which the primordial (scalar) power spectrum is sharply reduced by about 20%.

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“…Note that, in turn, this procedure provides the minimum number of rotations which are needed to fullfill the requirement 8 The smoothing is applied in order to minimise aliasing effects when going from real to harmonic space and vice versa. 9 In other words, we apply Nrot times Eq. (A.1).…”

Section: A Generating the Rotationsmentioning

confidence: 99%

Is the lack of power anomaly in the CMB correlated with the orientation of the Galactic plane?

Natale

Gruppuso

Molinari

et al. 2019

J. Cosmol. Astropart. Phys.

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The lack of power at large angular scales in the CMB temperature anisotropy pattern is a feature known to depend on the size of the Galactic mask. Not only the large scale anisotropy power in the CMB is lower than the best-fit ΛCDM model predicts, but most of the power seems to be localised close to the Galactic plane, making high-Galactic latitude regions more anomalous. We assess how likely the latter behaviour is in a ΛCDM model by extracting simulations from the Planck 2018 fiducial model. By comparing the former to Planck data in different Galactic masks, we reproduce the anomaly found in previous works, at a statistical significance of ∼ 3 σ. This result suggests the existence of a bizzarre correlation between the particular orientation of the Galaxy and the lack of power anomaly. To test this hypothesis, we perform random rotations of the Planck 2018 data and compare these to similarly rotated ΛCDM realisations. We find that, among all possible rotations, the lower-tail probability of the observed high-Galactic latitude data variance is still low at the level of 2.8 σ. Furthermore, the lowering trend of the variance when moving from low-to high-Galactic latitude is anomalous in the data at ∼ 3 σ when comparing to ΛCDM rotated realisations. This shows that the lack of power at high Galactic latitude is substantially stable against the "look elsewhere" effect induced by random rotations of the Galaxy orientation. Moreover, this analysis turns out to be substantially stable if we employ, in place of generic ΛCDM simulations, a specific set whose variance is constrained to reproduce the observed data variance.

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Covariance of CMB anomalies

Cited by 44 publications

References 68 publications

Joint Bayesian analysis of large angular scale CMB temperature anomalies

Joint Bayesian analysis of large angular scale CMB temperature anomalies

Modeling the large-scale power deficit with smooth and discontinuous primordial spectra

Is the lack of power anomaly in the CMB correlated with the orientation of the Galactic plane?

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