CMB polarization as a probe of the anomalous nature of the Cold Spot

TL;DR

This paper investigates the polarization signatures of the Cold Spot in the CMB to determine if it is caused by a cosmic texture or a Gaussian fluctuation, proposing a methodology to distinguish these scenarios with current and future experiments.

Contribution

It introduces a method to differentiate between a cosmic texture and a Gaussian fluctuation as the origin of the Cold Spot using polarization data, analyzing the discrimination power of various experiments.

Findings

Planck can reject the Gaussian hypothesis at ~7% significance.

QUIJOTE could provide a ~1% significance level.

Combined analysis enhances rejection significance to below 0.125%.

Abstract

One of the most interesting explanations for the non-Gaussian Cold Spot (CS) detected in the WMAP data by Vielva et al. 2004, is that it arises from the interaction of the CMB radiation with a cosmic texture (Cruz et al. 2007b). In this case, a lack of polarization is expected in the region of the spot, as compared to the typical values associated to large fluctuations of a GIRF. In addition, other physical processes related to a non-linear evolution of the gravitational field could lead to a similar scenario. However, some of these alternative scenarios (e.g., a large void in the large scale structure) have been shown to be very unlikely. In this work we characterise the polarization properties of the Cold Spot under both hypotheses: a large Gaussian spot and an anomalous feature generated, for instance, by a cosmic texture. We propose a methodology to distinguish between them, and we discuss its discrimination power as a function of the instrumental noise level. In particular, we address the cases of current experiments, like WMAP and Planck, and others in development as QUIJOTE. We find that for an ideal experiment the Gaussian hypothesis could be rejected at a significance level better than 0.8%. While WMAP is far from providing useful information in this respect, we find that Planck will be able to reach a significance of around 7%; in addition, we show that the ground-based experiment QUIJOTE could provide a significance of around 1%. If these results are combined with the significance level found for the CS in temperature, the capability of QUIJOTE and Planck to reject the alternative hypothesis becomes 0.025% and 0.124%, respectively.