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

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 $10^{-27}\mathrm{eV}$ to $10^{-23}\mathrm{eV}$) 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 $\hat{I}{\cdot }_a=\hat{I}{\text{c◯}}_{\mathrm{axion}}/\hat{I}{\text{c◯}}_{\mathrm{DM}}$ as low as $\sim 5\%$ if $m_a\simeq 10^{-27}\mathrm{eV}$ (at 95\% C.L.), with sensitivity extending up to $m_a\simeq 10^{-25}\mathrm{eV}$. If reionization and the primary CMB can be adequately modeled, Ostriker-Vishniac measurements could probe values $\hat{I}{\cdot }_a\simeq 10^{-3}$ if $10^{-27}\mathrm{eV}\lesssim m_a\lesssim 10^{-24}\mathrm{eV}$, or $\hat{I}{\cdot }_a\simeq 1$ if $m_a\simeq 10^{-22}\mathrm{eV}$, within the fuzzy dark matter window.

32 pages, 19 figures, 2 tables, published in PRD, comments welcome