Large Scale Anomalies in the Microwave Background: Causation and Correlation

TL;DR

This paper explores physical models of early universe inhomogeneities to explain large-scale anomalies in the microwave background, linking anomalies with polarization, structure, and inhomogeneity effects, and offers a framework for quantitative analysis.

Contribution

It introduces a physical modeling approach to large-scale anomalies, connecting anomalies with inhomogeneities and polarization, and demonstrates how a single plane wave can explain observed asymmetries.

Findings

Inhomogeneities can produce observable anomalies in the microwave background.

A single large plane wave inhomogeneity can account for low-l mode alignment.

The apparent spatial curvature from inhomogeneities is typically small.

Abstract

Most treatments of large scale anomalies in the microwave sky are a posteriori, with unquantified look-elsewhere effects. We contrast these with physical models of specific inhomogeneities in the early universe which then generate apparent anomalies. Physical models predict correlations between candidate anomalies, as well as the corresponding signals in polarization and large scale structure, reducing the impact of cosmic variance. We compute the apparent spatial curvature associated with large-scale inhomogeneities and show that it is typically small, allowing for a self-consistent analysis. Focussing on a single large plane wave inhomogeneity, we show this can contribute to low-l mode alignment and odd-even asymmetry in the power spectra and the best fit inhomogeneity accounts for a significant part of the claimed odd-even asymmetry. We argue that this approach can be generalized to provide a more quantitative assessment of potential large scale anomalies in the universe.