Searching for signatures of fuzzy dark matter in cosmic filament profiles
Current observations reveal persistent tensions with the standard cold dark matter paradigm, raising the question of whether these can be explained by baryonic physics alone or require alternative dark matter models. One such alternative is fuzzy (or wave) dark matter, consisting of ultralight particles with mass $m \sim 10^{-22}$ eV and de Broglie wavelengths on kpc to Mpc scales, which may give rise to large--scale interference patterns in non-linear structures around the cosmic web, such as filaments and clusters. In this work, we search for possible signatures of these interference fringes by investigating periodicities in the distribution of galaxies around cosmic web filaments. To demonstrate our methodology, we compare the filament profiles to a simple model that includes a periodic component of the form $A\cos(2πd/ λ)$, where $A$ is the maximum density contrast (amplitude) of the periodic component, with wavelength $λ=λ_0 \cosθ$ for some face-on wavelength $λ_0$ inclined at an angle $θ$ to the line of sight. Exploiting the large Sloan Digital Sky Survey (SDSS) Main Galaxy Sample, we analyse a sample of 4,394 filaments from the Tempel et al. filament catalogue, each containing at least 10 member galaxies. We find a vast portion of the parameter space is consistent with the observations at the $2σ$ level, including all models with $A = 0$ (no periodicity). We identify a region of the parameter space in tension with the observations, allowing us to exclude values of $A > 0.16 λ_0 + 0.18$ for $0.2\,\text{Mpc}\,\lesssim λ_0 \lesssim 2\,\text{Mpc}$ at the $3σ$ level, demonstrating the ability to test models of filament dark matter structure using this methodology.