The inflationary origin of the Cold Spot anomaly

TL;DR

This paper proposes a localized inhomogeneous reheating model to explain the Cold Spot anomaly in the CMB, suggesting it results from large-scale non-gaussianity possibly caused by an overdensity or supervoid.

Contribution

It introduces a new localized reheating scenario that can generate large-scale non-gaussianity, providing a physical explanation for the Cold Spot anomaly.

Findings

The model can explain the Cold Spot as an overdensity in the last scattering surface.

The mechanism may also account for the rarity of the supervoid.

It offers a feasible physical process for localized non-gaussianity in the CMB.

Abstract

Single-field inflation, arguably the simplest and most compelling paradigm for the origin of our Universe, is strongly supported by the recent results of the Planck satellite and the BICEP2 experiment. The results from Planck, however, also confirm the presence of a number of anomalies in the Cosmic Microwave Background (CMB), whose origin becomes problematic in single-field inflation. Among the most prominent and well-tested of these anomalies is the Cold Spot, which constitutes the only significant deviation from gaussianity in the CMB. Planck's non-detection of primordial non-gaussianity on smaller scales thus suggests the existence of a physical mechanism whereby significant non-gaussianity is generated on large angular scales only. In this letter, we address this question by developing a localized version of the inhomogeneous reheating scenario, which postulates the existence of a scalar field able to modify the decay of the inflaton on localized spatial regions only. We demonstrate that if the Cold Spot is due to an overdensity in the last scattering surface, the localization mechanism offers a feasible explanation for it, thus providing a physical mechanism for the generation of localized non-gaussianity in the CMB. If, on the contrary, the Cold Spot is caused by a newly discovered supervoid (as recently claimed), we argue that the localization mechanism, while managing to enhance underdensities, may well shed light on the rarity of the discovered supervoid.