Wave Dark Matter

Abstract

We review the physics and phenomenology of wave dark matter: a bosonic dark matter candidate lighter than about 30 eV. Such particles have a de Broglie wavelength exceeding the average inter-particle separation in a galaxy like the Milky Way, thus well described as a set of classical waves. We outline the particle physics motivations for them, including the QCD axion as well as ultra-light axion-like-particles such as fuzzy dark matter. The wave nature of the dark matter implies a rich phenomenology:• Wave interference gives rise to order unity density fluctuations on de Broglie scale in halos. One manifestation is vortices where the density vanishes and around which the velocity circulates. There is one vortex ring per de Broglie volume on average. • For sufficiently low masses, soliton condensation occurs at centers of halos. The soliton oscillates and random walks, another manifestation of wave interference. The halo and subhalo abundance is expected to be suppressed at small masses, but the precise prediction from numerical wave simulations remains to be determined. • For ultra-light ∼ 10 −22 eV dark matter, the wave interference substructures can be probed by tidal streams/gravitational lensing. The signal can be distinguished from that due to subhalos by the dependence on stream orbital radius/image separation. • Axion detection experiments are sensitive to interference substructures for wave dark matter that is moderately light. The stochastic nature of the waves affects the interpretation of experimental constraints and motivates the measurement of correlation functions.Current constraints and open questions, covering detection experiments and cosmological/galactic/black-hole observations, are discussed.

Schrödinger-Poisson Solitons: Perturbation Theory

“…Structure formation with ULDM reproduces the successes of ΛCDM on large scales while producing cored halos and substructure that are potentially more consistent with observations on small scales [8,11,12]. In addition to dark matter, the Schrödinger-Poisson system of equations governing ULDM dynamics emerges in other systems of interest, including boson stars [13][14][15][16] and the very early universe [17][18][19].…”

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

“…Fuzzy dark matter (FDM) is an alternative to CDM [2][3][4]. In this model, DM is composed of ultra-light particles with mass as light as 10 −22 eV.…”

Galactic rotation curves versus ultralight dark matter: A systematic comparison with SPARC data

“…The QPs arise from interference patterns in the field, with a characteristic coherence length of λ dB ∼ 2π/(mσ). If the ULDM ambient density is ρ, the mass of each QP is of order M QP ∼ (4π/3)ρλ 3 dB ∼ 6 × 10 9 ρ/0.1 M pc −3 50 kms −1 /σ 3 10 −22 eV/m 3 M .…”

“…The wave nature of such ultralight dark matter (ULDM) may manifest itself in a variety of astrophysical settings . A wide range of the particle mass, 10 −25 m 10 −19 eV, can be probed via observations of galaxies [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]36] (for reviews, see [3,24]). At the lower end in m, Ref.…”