Structure formation in fuzzy dark matter

Structure formation in fuzzy dark matter

PI: Anastasia Fialkov

Filamentary network in FDM. Figure from Dome et al. 2023b.

The fuzzy dark matter (FDM) scenario has received increased attention in recent years due to the small-scale challenges of the LCDM cosmological model and the lack of any experimental evidence for any candidate particle. In this DiRAC project, we use cosmological N-body simulations to investigate large-scale structure in FDM cosmologies. In Dome et al. 2023 we study halo density profiles, shapes and alignments in FDM-like cosmologies (the latter two for the first time) by providing fits and quantifying departures from LCDM as a function of the FDM particle mass m. We explore halo shapes finding that in FDM-like cosmologies halos are more elongated around the virial radius than their LCDM counterparts. We also consider intrinsic alignment correlations, stemming from the deformation of initially spherically collapsing halos in an ambient gravitational tidal field, and find that they become stronger with decreasing m. 

A follow-up project considers cosmic web structure. On large cosmological scales, anisotropic gravitational collapse is manifest in the dark cosmic web. Its statistical properties are well known for the standard CDM cosmology, yet become modified for alternative dark matter models such as FDM. In a paper submitted in February 2023 to MNRAS (Dome et al. 2023b) we assess for the first time the relative importance of cosmic nodes, filaments, walls, and voids in cosmology with small-scale suppression of power (such as FDM). We explore cosmic web by applying the NEXUS+ Multiscale Morphology Filter technique to cosmological N-body simulations. We quantify the mass and volume filling fractions of cosmic environments (nodes, filaments, walls, voids) at redshifts z=3.4-5.6.

Cosmological Simulation of Fuzzy Dark Matter with Self-Interaction

In this DiRAC project we investigate cosmological structure formation in Fuzzy Dark Matter (FDM) with an attractive self-interaction (SI) using numerical simulations. Such a SI would arise if the FDM boson were an ultralight axion, which has a strong CP symmetry-breaking scale (decay constant). Although weak, the attractive SI may be strong enough to counteract the quantum `pressure’ and alter structure formation. We find in our simulations that the SI can enhance small-scale structure formation, and soliton cores above a critical mass undergo a phase transition, transforming from dilute to dense solitons. The results are summarized in Mocz et al. accepted for publication in MNRAS in February 2023.

Figure from Mocz et al. 2023. Projected dark matter densities at z = 2, with blue arrows denoting formed solitons.

Exploring Star-Forming Regions in Fuzzy Dark Matter Models

To complement the large-scale simulations done in the framework of ACSP253 project we have run a set of small-scale hydrodynamical simulations of Fuzzy Dark Matter (FDM) using a Schrodinger-Poisson solver (developed by Mocz). We will use the complete set of simulations to explore first galaxy formation for different FDM masses and make predictions for the 21-cm signal of neutral hydrogen at cosmic dawn.