Non-linear hydrodynamics of axion dark matter: relative velocity effects and "quantum forces"

Abstract

The non-linear hydrodynamic equations for axion/scalar field dark matter (DM) in the non-relativistic Madelung-Shcrödinger form are derived in a simple manner, including the effects of universal expansion and Hubble drag. The hydrodynamic equations are used to investigate the relative velocity between axion DM and baryons, and the moving-background perturbation theory (MBPT) derived. Axions massive enough to be all of the DM do not affect the coherence length of the relative velocity, but the MBPT equations are modified by the inclusion of the axion effective sound speed. These MBPT equations are necessary for accurately modelling the effects of axion DM on the formation of the first cosmic structures, and suggest that the 21cm power spectrum could improve constraints on axion mass by up to four orders of magnitude with respect to the current best constraints. A further application of these results uses the "quantum force" analogy to model scalar field gradient energy in a smoothed-particle hydrodynamics model of axion DM. Such a model can treat axion DM in the non-linear regime and could be incorporated into existing N-body codes.

8 pages, 3 figures. v2: longer discussion of SPH smoothing. v3: some discussion added, published in PRD

References in corpus (10)

• Cosmic Structure as the Quantum Interference of a Coherent Dark Wave
• The Effective Field Theory of Cosmological Large Scale Structures
• Discovering the QCD Axion with Black Holes and Gravitational Waves
• A search for ultra-light axions using precision cosmological data
• Dwarf galaxies in CDM and SIDM with baryons: observational probes of the nature of dark matter
• Ultra-Light Scalar Fields and the Growth of Structure in the Universe
• Galaxy UV-luminosity function and reionization constraints on axion dark matter
• Axion as a Cold Dark Matter candidate
• Large-scale BAO signatures of the smallest galaxies
• Supersonic Relative Velocity between Dark Matter and Baryons: A Review

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