Analyzing the cosmic variance limit of remote dipole measurements of the cosmic microwave background using the large-scale kinetic Sunyaev Zel'dovich effect

TL;DR

This paper explores how cross-correlating the large-scale kinetic Sunyaev Zel'dovich effect with large-scale structure surveys can surpass cosmic variance limits of the primary CMB, enabling better insights into cosmic inhomogeneities.

Contribution

It introduces a method using kSZ tomography to access more large-scale modes than the primary CMB, with detailed calculations and forecasts for future experiments.

Findings

Significant signal-to-noise ratio over various multipoles and bin configurations.

kSZ tomography can access more modes than primary CMB on similar scales.

First detection feasible with upcoming CMB and galaxy surveys.

Abstract

Due to cosmic variance we cannot learn any more about large-scale inhomogeneities from the primary cosmic microwave background (CMB) alone. More information on large scales is essential for resolving large angular scale anomalies in the CMB. Here we consider cross correlating the large-scale kinetic Sunyaev Zel'dovich (kSZ) effect and probes of large-scale structure, a technique known as kSZ tomography. The statistically anisotropic component of the cross correlation encodes the CMB dipole as seen by free electrons throughout the observable Universe, providing information about long wavelength inhomogeneities. We compute the large angular scale power asymmetry, constructing the appropriate transfer functions, and estimate the cosmic variance limited signal to noise for a variety of redshift bin configurations. The signal to noise is significant over a large range of power multipoles and numbers of bins. We present a simple mode counting argument indicating that kSZ tomography can be used to estimate more modes than the primary CMB on comparable scales. A basic forecast indicates that a first detection could be made with next-generation CMB experiments and galaxy surveys. This paper motivates a more systematic investigation of how close to the cosmic variance limit it will be possible to get with future observations.