Ultra-light axions and the kinetic Sunyaev-Zel'dovich Effect

TL;DR

This paper investigates how ultra-light axion dark matter influences the kinetic Sunyaev-Zel'dovich effect in the cosmic microwave background, providing new analytic tools and forecasts for future surveys to constrain axion properties.

Contribution

It introduces new analytic expressions for pairwise velocities and Ostriker-Vishniac signatures to assess ULA impacts on kSZ observables, extending the methodology for dark matter constraints.

Findings

Future CMB-S4 and DESI surveys can detect ULA fractions as low as 5% for certain masses.

Ostriker-Vishniac measurements could probe ULA fractions down to 0.1% within specific mass ranges.

Sensitivity extends to ULA masses up to 10^{-25} eV, covering the fuzzy dark matter window.

Abstract

Measurements of secondary cosmic microwave background (CMB) anisotropies, such as the Sunyaev-Zel'dovich (SZ) effect, will enable new tests of neutrino and dark sector properties. The kinetic SZ (kSZ) effect is produced by cosmological flows, probing structure growth. Ultra-light axions (ULAs) are a well-motivated dark-matter candidate. Here the impact of ULA dark matter (with mass $10^{-27}~{\rm eV}$ to $10^{-23}~{\rm eV}$) on kSZ observables is determined, applying new analytic expressions for pairwise cluster velocities and Ostriker-Vishniac signatures in structure-suppressing models. For the future CMB-S4 and ongoing DESI galaxy surveys, the kSZ effect (along with primary anisotropies) will probe ULA fractions $\eta_a = \Omega_{\rm{axion}}/\Omega_{\rm DM}$ as low as $\sim 5\%$ if $m_{a}\simeq 10^{-27}~{\rm eV}$ (at 95\% C.L.), with sensitivity extending up to $m_{a}\simeq 10^{-25}~{\rm eV}$. If reionization and the primary CMB can be adequately modeled, Ostriker-Vishniac measurements could probe values $\eta_{a}\simeq 10^{-3}$ if $10^{-27}~{\rm eV}\lesssim m_{a}\lesssim 10^{-24}~{\rm eV}$, or $\eta_{a}\simeq 1$ if $m_{a}\simeq 10^{-22}~{\rm eV}$, within the fuzzy dark matter window.