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We study the implications of relaxing the requirement for ultralight axions to account for all dark matter in the Universe by examining mixed dark matter (MDM) cosmologies with axion fractions |$f \le 0.3$| within the fuzzy dark matter window |$10^{-25}$|  eV |$\lesssim m \lesssim 10^{-23}$|  eV. Our simulations, using a new MDM gravity solver implemented in AxiREPO , capture wave dynamics across various scales with high accuracy down to redshifts |$z\approx 1$|⁠. We identify haloes with Rockstar using the cold dark matter component and find good agreement of inferred halo mass functions and concentration–mass relations with theoretical models across redshifts |$z=1{\!-\!}10$|⁠. This justifies our halo finder approach a posteriori as well as the assumptions underlying the MDM halo model AxionHMcode. Using the inferred axion halo mass–cold halo mass relation |$M_{\text{a}}(M_{\text{c}})$| and calibrating a generalized smoothing parameter |$\alpha$| to our MDM simulations, we present a new version of AxionHMcode. The code exhibits excellent agreement with simulations on scales |$k\lt 20 \, h \, \text{cMpc}^{-1}$| at redshifts |$z=1{\!-\!}3.5$| for |$f\le 0.1$| around the fiducial axion mass |$m = 10^{-24.5}\, \text{eV} = 3.16\times 10^{-25}\, \text{eV}$|⁠ , with maximum deviations remaining below 10 per cent. For axion fractions |$f\le 0.3$|⁠ , the model maintains accuracy with deviations under 20 per cent at redshifts |$z\approx 1$| and scales |$k\lt 10 \, h \, \text{cMpc}^{-1}$|⁠ , though deviations can reach up to 30 per cent for higher redshifts when |$f=0.3$|⁠. Reducing the run-time for a single evaluation of AxionHMcode to below 1 min, these results highlight the potential of AxionHMcode to provide a robust framework for parameter sampling across MDM cosmologies in Bayesian constraint and forecast analyses. [ABSTRACT FROM AUTHOR]

Fuzzy dark matter (FDM) is a dark matter candidate consisting of ultralight scalar particles with masses around |$10^{-22}\, \mathrm{eV}/c^2$|⁠ , a regime where cold bosonic matter behaves as a collective wave rather than individual particles. Although constraints on FDM are accumulating in many different contexts, very few have been verified by self-consistent numerical simulations. We present new large numerical simulations of cosmic structure formation with FDM, solving the full Schrödinger–Poisson (SP) equations using the AxiREPO code, which implements a pseudo-spectral numerical method. Combined with our previous simulations, they allow us to draw a four-way comparison of matter clustering, contrasting results (such as power spectra) for each combination of initial conditions (ICs; FDM versus cold dark matter, CDM) and dynamics (SP versus N -body). By disentangling the impact of ICs and non-linear dynamics in this manner, we can gauge the validity of approximate methods used in previous works, such as ordinary N -body simulations with an FDM initial power spectrum. Due to the comparatively large volume achieved in our FDM simulations, we are able to measure the FDM halo mass function from full wave simulations for the first time, and compare to previous results obtained using analytic or approximate approaches. We also investigate the density profiles of these filaments and compare to their ΛCDM counterparts. [ABSTRACT FROM AUTHOR]

In the fuzzy dark matter (FDM) model, gravitationally collapsed objects always consist of a solitonic core located within a virialized halo. Although various numerical simulations have confirmed that the collapsed structure can be described by a cored Navarro–Frenk–White-like density profile, there is still disagreement about the relation between the core mass and the halo mass. To fully understand this relation, we have assembled a large sample of cored haloes based on both idealized soliton mergers and cosmological simulations with various box sizes. We find that there exists a sizeable dispersion in the core–halo mass relation that increases with halo mass, indicating that the FDM model allows cores and haloes to coexist in diverse configurations. We provide a new empirical equation for a core–halo mass relation with uncertainties that can encompass all previously found relations in the dispersion, and emphasize that any observational constraints on the particle mass m using a tight one-to-one core–halo mass relation should suffer from an additional uncertainty of the order of 50  per cent for halo masses |${\gtrsim} 10^9 \, [8\times 10^{-23} \, \mathrm{eV}/(mc^2)]^{3/2} \, \mathrm{M}_\odot$|⁠. We suggest that tidal stripping may be one of the effects contributing to the scatter in the relation. [ABSTRACT FROM AUTHOR]

An ultralight bosonic particle of mass around |$10^{-22}\, \mathrm{eV}/c^2$| is of special interest as a dark matter candidate, as it both has particle physics motivations, and may give rise to notable differences in the structures on highly non-linear scales due to the manifestation of quantum-physical wave effects on macroscopic scales, which could address a number of contentious small-scale tensions in the standard cosmological model, ΛCDM. Using a spectral technique, we here discuss simulations of such fuzzy dark matter (FDM), including the full non-linear wave dynamics, with a comparatively large dynamic range and for larger box sizes than considered previously. While the impact of suppressed small-scale power in the initial conditions associated with FDM has been studied before, the characteristic FDM dynamics are often neglected; in our simulations, we instead show the impact of the full non-linear dynamics on physical observables. We focus on the evolution of the matter power spectrum, give first results for the FDM halo mass function directly based on full FDM simulations, and discuss the computational challenges associated with the FDM equations. FDM shows a pronounced suppression of power on small scales relative to cold dark matter (CDM), which can be understood as a damping effect due to 'quantum pressure'. In certain regimes, however, the FDM power can exceed that of CDM, which may be interpreted as a reflection of order-unity density fluctuations occurring in FDM. In the halo mass function, FDM shows a significant abundance reduction below a characteristic mass scale only. This could in principle alleviate the need to invoke very strong feedback processes in small galaxies to reconcile ΛCDM with the observed galaxy luminosity function, but detailed studies that also include baryons will be needed to ultimately judge the viability of FDM. [ABSTRACT FROM AUTHOR]