Testing cosmological models with large-scale power modulation using microwave background polarization observations

TL;DR

This paper investigates how future large-scale CMB polarization observations can help detect and understand large-scale power modulation anomalies, using a systematic mode analysis to optimize information extraction.

Contribution

It introduces a method to maximize information from polarization data by generalizing the Karhunen-Loeve transform, accounting for temperature data constraints, to detect primordial power modulation.

Findings

A 60% sky polarization map can detect modulation at 3σ level.

Most information is contained in a single optimal mode.

Polarization data can complement temperature data in anomaly detection.

Abstract

We examine the degree to which observations of large-scale cosmic microwave background (CMB) polarization can shed light on the puzzling large-scale power modulation in maps of CMB anisotropy. We consider a phenomenological model in which the observed anomaly is caused by modulation of large-scale primordial curvature perturbations, and calculate Fisher information and error forecasts for future polarization data, constrained by the existing CMB anisotropy data. Because a significant fraction of the available information is contained in correlations with the anomalous temperature data, it is essential to account for these constraints. We also present a systematic approach to finding a set of normal modes that maximize the available information, generalizing the well-known Karhunen-Loeve transformation to take account of the constraints from the temperature data. A polarization map covering at least $\sim 60\%$ of the sky should be able to provide a $3\sigma$ detection of modulation at the level favored by the temperature data. A significant fraction of the information in such a data set is contained in the single mode that optimally encapsulates the signal due to temperature-polarization correlation.