Interference in fuzzy dark matter filaments

Idealized models and statistics

¹ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, Blindern, 0315 Oslo, Norway
² Theoretical Particle Physics and Cosmology, King’s College London, Strand, London WC2R 2LS, UK
³ Department of Physics, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
⁴ Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George St., Toronto, ON M5S 3H4, Canada

^⋆ Corresponding author; timzi@uio.no

Received: 23 February 2025
Accepted: 6 March 2025

Abstract

Fuzzy (wave) dark matter (FDM), the dynamical model underlying an ultralight bosonic dark matter species, produces a rich set of nongravitational signatures that distinguishes it markedly from the phenomenologically related warm (particle) dark matter (WDM) scenario. The emergence of extended interference fringes hosted by cosmic filaments is one such phenomenon reported by cosmological simulations, and a detailed understanding of such may strengthen existing limits on the boson mass but also break the degeneracy with WDM, and provide a unique fingerprint of interference in cosmology. In this paper, we provide initial steps toward this goal. In particular, we show in a bottom-up approach, how the presence of interference in an idealized filament population can lead to a non-suppressive feature in the matter power spectrum – an observation supported by cosmological FDM simulations. To this end, we build on a theoretically motivated and numerically observed steady-state approximation for filaments and express the equilibrium dynamics of such in an expansion of FDM eigenstates. We optimize the size of the expansion by incorporating classical phase-space information. Ellipsoidal collapse considerations were used to construct a fuzzy filament mass function which, together with the reconstructed FDM wave function, allowed us to efficiently compute the one-filament power spectrum. We showcase our non-perturbative interference model for a selection of boson masses and confirm our approach is able to produce the matter power boost observed in fully cosmological FDM simulations. More precisely, we find an excess in correlation between the spatial scale associated with the FDM ground state and the quantum pressure scale. We speculate about applications of this effect in data analysis.