Measuring the Small-Scale Matter Power Spectrum with High-Resolution CMB Lensing

TL;DR

This paper proposes a method using high-resolution CMB lensing measurements to probe the small-scale matter power spectrum, potentially distinguishing between different dark matter models with high significance.

Contribution

It introduces a novel approach to measure small-scale matter distribution via CMB lensing at unprecedented resolution, enabling discrimination between dark matter scenarios.

Findings

A 4,000 sq. degree survey with 0.5 uK-arcmin sensitivity can distinguish dark matter models at 4-sigma.

Higher sensitivity (0.1 uK-arcmin) improves significance to over 20-sigma.

Systematic effects can be mitigated, making next-generation CMB lensing a robust tool.

Abstract

We present a method to measure the small-scale matter power spectrum using high-resolution measurements of the gravitational lensing of the Cosmic Microwave Background (CMB). To determine whether small-scale structure today is suppressed on scales below 10 kiloparsecs (corresponding to M < 10^9 M_sun), one needs to probe CMB-lensing modes out to L ~ 35,000, requiring a CMB experiment with about 20 arcsecond resolution or better. We show that a CMB survey covering 4,000 square degrees of sky, with an instrumental sensitivity of 0.5 uK-arcmin at 18 arcsecond resolution, could distinguish between cold dark matter and an alternative, such as 1 keV warm dark matter or 10^(-22) eV fuzzy dark matter with about 4-sigma significance. A survey of the same resolution with 0.1 uK-arcmin noise could distinguish between cold dark matter and these alternatives at better than 20-sigma significance; such high-significance measurements may also allow one to distinguish between a suppression of power due to either baryonic effects or the particle nature of dark matter, since each impacts the shape of the lensing power spectrum differently. CMB temperature maps yield higher signal-to-noise than polarization maps in this small-scale regime; thus, systematic effects, such as from extragalactic astrophysical foregrounds, need to be carefully considered. However, these systematic concerns can likely be mitigated with known techniques. Next-generation CMB lensing may thus provide a robust and powerful method of measuring the small-scale matter power spectrum.