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 eV to 10 −23 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 ηa = Ωaxion/ΩDM as low as ∼ 5% if ma 10 −27 eV (at 95% C.L.), with sensitivity extending up to ma 10 −25 eV. If reionization and the primary CMB can be adequately modeled, Ostriker-Vishniac measurements could probe values ηa 10 −3 if 10 −27 eV ma 10 −24 eV, or ηa 1 if ma 10 −22 eV, within the fuzzy dark matter window.

Exploring delaying and heating effects on the 21-cm signature of fuzzy dark matter

“…Upcoming "high definition CMB" experiments show a similar level of sensitivity [17]. Measurements of the cluster pairwise velocity dispersion using the kinetic Sunyaev-Zel'dovich (kSZ) effect could reach the FDM mass limit as low as ∼ 10 −27 eV [18]. Future pulsar timing array measurements could probe FDM masses around ∼ 10 −22 eV [19].…”

“…In the FDM paradigm, halos above the suppression mass cannot collapse before a certain redshift and thus galaxy formation is delayed. Therefore, we can expect this signature of FDM to be found in direct observations of cosmic dawn (CD) and the epoch of reionization (EoR) via the neutral Hydrogen (H I) 21-cm global signal and its fluctuations [9], complementing other FDM probes [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24].…”

Dark Matter Physics from the CMB-S4 Experiment

“…In turquoise, UDM parameter space probed by kinetic Sunyaev-Zel'dovich measurements combining CMB-S4 data (including primary anisotropies) with large-scale structure information from the Dark Energy Spectroscopic Instrument (kSZ-S4) [128]; in blue, forecast CMB-S4 UDM sensitivity using temperature, polarization and lensing data [146]; in green, forecast Ostriker-Vishniac effect bounds from CMB-S4 (OV-S4) [128]. Existing CMB bounds come from Planck [114,148], while LSS bounds come from galaxy clustering combined with Planck (+BOSS) [149], galaxy weak lensing combined with Planck (+DES) [150], the UV luminosity function and optical depth to reionization (Rei.)…”

“…When this occurs in galaxy clusters, the resulting kinetic Sunyaev-Zel'dovich (kSZ) induces additional CMB temperature anisotropies that probe the real-time growth of structure, and can be detected via cross-correlation with galaxy surveys. ULAs will boost this signal (due to increased bias in a structure-suppressing cosmology), yielding a potential improvement in sensitivity [128]. Even better sensitivity is possible using the Ostriker-Vishniac (OV) CMB anisotropies, induced by gas inhomogeneities during the mildly non-linear reionization epoch.…”

Accurate effective fluid approximation for ultralight axions

“…This difficulty is usually addressed with an effective * samuel.passaglia@ipmu.jp fluid approximation (EFA) that replaces the exact Klein-Gordon solution for the field by effectively averaging over the axion oscillations [19,[21][22][23]. This approximation inevitably induces errors when making predictions for observables because the axion field is initially effectively frozen and the approximate equations of state used to evolve the effective fluid efficiently may then be insufficiently accurate.…”