Large-Angle CMB Suppression and Polarization Predictions

TL;DR

This paper investigates the large-angle CMB suppression anomaly by proposing polarization-based tests, especially using the temperature-$Q$ correlation, to determine if the anomaly is a rare fluctuation within the standard cosmological model.

Contribution

It introduces a new statistical method based on temperature-$Q$ correlation to test the anomaly hypothesis in CMB polarization data.

Findings

A specific $TQ$ correlation statistic can reject the anomaly hypothesis with high confidence.

The proposed test has a 25% chance of excluding the LCDM model at 99.9% confidence.

Polarization observations can provide critical insights into the large-angle CMB anomaly.

Abstract

The anomalous lack of large angle temperature correlations has been a surprising feature of the cosmic microwave background (CMB) since first observed by COBE-DMR and subsequently confirmed and strengthened by the Wilkinson Microwave Anisotropy Probe. This anomaly may point to the need for modifications of the standard model of cosmology or may indicate that our Universe is a rare statistical fluctuation within that model. Further observations of the temperature auto-correlation function will not elucidate the issue; sufficiently high precision statistical observations already exist. Instead, alternative probes are required. In this work we explore the expectations for forthcoming polarization observations. We define a prescription to test the hypothesis that the large-angle CMB temperature perturbations in our Universe represent a rare statistical fluctuation within the standard cosmological model. These tests are based on the temperature-$Q$ Stokes parameter correlation. Unfortunately these tests cannot be expected to be definitive. However, we do show that if this $TQ$-correlation is observed to be sufficiently large over an appropriately chosen angular range, then the hypothesis can be rejected at a high confidence level. We quantify these statements and optimize the statistics we have constructed to apply to the anticipated polarization data. We find that we can construct a statistic that has a 25 per cent chance of excluding the hypothesis that we live in a rare realization of LCDM at the 99.9 per cent confidence level.