Testing physical models for dipolar asymmetry: from temperature to k space to lensing

TL;DR

This paper investigates a physical model for the large-scale dipolar asymmetry in the CMB by analyzing its effects in k space on temperature and lensing, highlighting the limitations of lensing data and the potential of polarization measurements.

Contribution

It introduces a k-space modulation framework for the CMB asymmetry and assesses its detectability using Planck data and polarization, clarifying constraints and future testing prospects.

Findings

CMB lensing alone cannot confirm or refute the modulation.

The asymmetry is weakly constrained by current data.

Polarization measurements could be more effective in testing the model.

Abstract

One of the most intriguing hints of a departure from the standard cosmological model is a large-scale dipolar power asymmetry in the cosmic microwave background (CMB). If not a statistical fluke, its origins must lie in the modulation of the position-space fluctuations via a physical mechanism, which requires the observation of new modes to confirm or refute. We introduce an approach to describe such a modulation in k space and calculate its effects on the CMB temperature and lensing. We fit the k-space modulation parameters to Planck 2015 temperature data and show that CMB lensing will not provide us with enough independent information to confirm or refute such a mechanism. However, our approach elucidates some poorly understood aspects of the asymmetry, in particular that it is weakly constrained. Also, it will be particularly useful in predicting the effectiveness of polarization in testing a physical modulation.