Using CMB polarization to constrain the anomalous nature of the Cold Spot with an incomplete sky-coverage

TL;DR

This study investigates the potential of CMB polarization data, even with incomplete sky coverage, to determine whether the Cold Spot anomaly is due to standard Gaussian fluctuations or alternative physical processes like topological defects.

Contribution

It extends previous full-sky analysis methods to partial-sky data, assessing the ability to distinguish between Gaussian and non-Gaussian origins of the Cold Spot using polarization patterns.

Findings

Ideal noise-free experiments can reject non-Gaussian scenarios at ~1% significance.

Realistic noise levels in QUIJOTE and Planck yield significance levels of 1.5% and 7.4%.

Application to WMAP data was inconclusive with a 32% significance level.

Abstract

Recent results of the ESA Planck satellite have confirmed the existence of some anomalies in the statistical distribution of the cosmic microwave background (CMB) anisotropies. One of the most intriguing anomalies is the Cold Spot, firstly detected in the WMAP data by Vielva et al. (2004). In a later paper, Vielva et al. (2011) developed a method to probe the anomalous nature of the Cold Spot by using the cross-correlation of temperature and polarization of the CMB fluctuations. Whereas this work was built under the assumption of analysing full-sky data, in the present paper we extend such approach to deal with realistic data sets with a partial sky-coverage. In particular, we exploit the radial and tangential polarization patterns around temperature spots. We explore the capacity of the method to distinguish between a standard Gaussian CMB scenario and an alternative one, in which the Cold Spot arises from a physical process that does not present correlated polarization features (e.g., topological defects), as a function of the instrumental-noise level. Moreover, we consider more in detail the case of an ideal noise-free experiment and those ones with the expected instrumental-noise levels in QUIJOTE and Planck experiments. We also present an application to the 9-year WMAP data, without being able to obtain firm conclusions, with a significance level of 32%. In the ideal case, the alternative scenario could be rejected at a significance level of around 1%, whereas for expected noise levels of QUIJOTE and Planck experiments the corresponding significance levels are 1.5% and 7.4%, respectively.