Estimators for CMB statistical anisotropy

By D. Hanson, A. Lewis. 2009

200 citations recorded by the source corpus.

We use quadratic maximum-likelihood (QML) estimators to constrain models with Gaussian but statistically anisotropic CMB fluctuations, using CMB maps with realistic sky-coverage and instrumental noise. This approach is optimal when the anisotropy is small, or when checking for consistency with isotropy. We demonstrate the power of the QML approach by applying it to the WMAP data to constrain several models which modulate the observed CMB fluctuations to produce a statistically anisotropic sky. We first constrain an empirically motivated spatial modulation of the observed CMB fluctuations, reproducing marginal evidence for a dipolar modulation pattern with amplitude 7% at l?60, but demonstrate that the effect decreases at higher multipoles and is ?1% at l~500. We also look for evidence of a direction-dependent primordial power spectrum, finding a very statistically significant quadrupole signal nearly aligned with the ecliptic plane; however we argue this anisotropy is largely contaminated by observational systematics. Finally, we constrain the anisotropy due to a spatial modulation of adiabatic and isocurvature primordial perturbations, and discuss the close relationship between anisotropy and non-Gaussianity estimators.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/538a984927219ac60beeea67eaca425a3782fc3d

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Citations in the corpus

Gauge fields and inflation (2012, background): “These observational signature, although their statistical significance is still controversial [41], stimulated activity in the research of statistical anisotropy [42, 43, 44, 45, 46, 47, 48, 49, 50, 51].”
Large-Angle Anomalies in the CMB (2010, methodology): “[42], building on the work of Groeneboom and Eriksen [43] and Hanson and Lewis [44] and motivated by a model due to Ackerman et al.”
SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP ) OBSERVATIONS: ARE THERE COSMIC MICROWAVE BACKGROUND ANOMALIES? (2010, methodology): “Comparing these methods, we find that the Hanson & Lewis (2009) optimal quadratic estimator has significant advantages over other analysis methods that have appeared in the literature.”
Planck 2015 results. XVII. Constraints on primordial non-Gaussianity (2015, unknown): “Optimal cubic bispectrum estimators were first discussed in Heavens (1998). It was then shown that, in the limit of small NG, the optimal polarized fNL estimator is described by (Creminelli et al.”
Probing cosmic isotropy with a new X-ray galaxy cluster sample through the LX–T scaling relation (2020, background): “…feature present in the CMB is the dipole power asymmetry detected in both WMAP and Planck with a significance of ∼ 2−3.5σ toward (l, b) ∼ (230◦,−20◦) (Eriksen et al. 2004; Hanson & Lewis 2009; Bennett et al. 2011; Akrami et al. 2014; Planck Collaboration XXIII 2014; Planck Collaboration XVI 2016).”
Planck 2018 results. IX. Constraints on primordial non-Gaussianity (2019, background): “CMB lensing generates a significant CMB bispectrum (Hanson & Lewis 2009; Mangilli & Verde 2009; Lewis et al. 2011; Mangilli et al. 2013).”
SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) OBSERVATIONS: COSMOLOGICAL INTERPRETATION (2010, background): “…parameters (fNL from the bispectrum), parity-violation angle (∆α from the TB and EB correlations), modulated primordial power spectrum (g(k) from direction-dependent power spectra; Ackerman et al. 2007; Hanson & Lewis 2009; Groeneboom et al. 2010, see Bennett et al. 2010 for the 7-year limits).”
Cosmology and Fundamental Physics with the Euclid Satellite (2012, background): “, [463] and [569] (or for LSS [592]) to explain the hemispherical asymmetry falls within the parametrization of Eq.”