Detecting the Cold Spot as a Void with the Non-Diagonal Two-Point Function

TL;DR

This paper proposes that the Cold Spot anomaly in the CMB could be caused by a large Void, and demonstrates that lensing effects produce a detectable signal in the non-diagonal two-point function, which Planck can test.

Contribution

It introduces a novel method using the non-diagonal two-point function to detect large Voids responsible for the Cold Spot in the CMB.

Findings

Lensing effects from a Void produce a significant signal in the non-diagonal two-point function.

Planck can confirm or rule out the Void hypothesis with high confidence.

The method is effective for any Void radius with a strong Signal-to-Noise ratio.

Abstract

The anomaly in the Cosmic Microwave Background known as the "Cold Spot" could be due to the existence of an anomalously large spherical (few hundreds Mpc/h radius) underdense region, called a "Void" for short. Such a structure would have an impact on the CMB also at high multipoles l through Lensing. This would then represent a unique signature of a Void. Modeling such an underdensity with an LTB metric, we show that the Lensing effect leads to a large signal in the non-diagonal two-point function, centered in the direction of the Cold Spot, such that the Planck satellite will be able to confirm or rule out the Void explanation for the Cold Spot, for any Void radius with a Signal-to-Noise ratio of at least O(10).