A Theory of a Spot

TL;DR

This paper proposes an inflationary model that creates large spherical bubbles affecting the CMB, potentially explaining the WMAP cold spot through specific imprints on the cosmic microwave background.

Contribution

It introduces a simple inflationary scenario producing large bubbles with distinct effects on the CMB, offering a possible explanation for the WMAP cold spot.

Findings

Bubbles can produce observable CMB anisotropies via Sachs-Wolfe and ISW effects.

Model can potentially explain the WMAP cold spot with moderate fine tuning.

Different bubble sizes imprint distinct secondary anisotropies on the CMB.

Abstract

We present a simple inflationary scenario that can produce arbitrarily large spherical underdense or overdense regions embedded in a standard Lambda cold dark matter paradigm, which we refer to as bubbles. We analyze the effect such bubbles would have on the Cosmic Microwave Background (CMB). For super-horizon sized bubble in the vicinity of the last scattering surface, a signal is imprinted onto CMB via a combination of Sach-Wolfe and an early integrated Sach-Wolfe (ISW) effects. Smaller, sub-horizon sized bubbles at lower redshifts (during matter domination and later) can imprint secondary anisotropies on the CMB via Rees-Sciama, late-time ISW and Ostriker-Vishniac effects. Our scenario, and arguably most similar inflationary models, produce bubbles which are over/underdense in potential: in density such bubbles are characterized by having a distinct wall with the interior staying at the cosmic mean density. We show that such models can potentially, with only moderate fine tuning, explain the \emph{cold spot}, a non-Gaussian feature identified in the Wilkinson Microwave Anisotropy Probe (WMAP) data by several authors. However, more detailed comparisons with current and future CMB data are necessary to confirm (or rule out) this scenario.