Non-Gaussianity in WMAP 5-year CMB map seen through Needlets

TL;DR

This paper uses needlets, a type of wavelet, to analyze WMAP 5-year CMB data, detecting non-Gaussian features and constraining the primordial non-Gaussianity parameter, revealing asymmetries in the bispectrum.

Contribution

The study introduces needlets for detailed non-Gaussianity analysis in CMB data, providing new constraints on primordial non-Gaussianity and identifying asymmetries.

Findings

Detected anomalous spots responsible for 50% of power asymmetry.

Constrained the non-Gaussianity parameter to $f_{NL}=21\u00b140.

Identified high asymmetry in the bispectrum, especially in isosceles configurations.

Abstract

The cosmic microwave background radiation is supposed to be Gaussian and this hypothesis is in good agreement with the recent very accurate measurements. Nonetheless a tiny amount of non-Gaussianity is predicted by the standard inflation scenario, while more exotic models suggest a higher degree of non-Gaussianity. Tightly constraining the level of Gaussianity in the CMB data represents then a fundamental handle to understand the physics and the origin of our universe. By means of needlets, a novel rendition of wavelets, characterised by excellent properties of localisations both in harmonic and pixel domain, we are able to detect anomalous spots in the southern hemisphere responsible for roughly the 50% of power asymmetry we measure in the CMB power spectrum, and to perform a detailed analysis of the needlets bispectrum. We then constrain the primordial non-Gaussianity parameter, $f{\rm NL}=21\pm40$ at 68% c.f., and spot a high asymmetry in the bispectrum, in particular in the isosceles configurations.