AxioNyx: Simulating Mixed Fuzzy and Cold Dark Matter

Abstract

The distinctive effects of fuzzy dark matter are most visible at non-linear galactic scales. We present the first simulations of mixed fuzzy and cold dark matter, obtained with an extended version of the Nyx code. Fuzzy (or ultralight, or axion-like) dark matter dynamics are governed by the comoving Schrödinger-Poisson equation. This is evolved with a pseudospectral algorithm on the root grid, and with finite differencing at up to six levels of adaptive refinement. Cold dark matter is evolved with the existing N-body implementation in Nyx. We present the first investigations of spherical collapse in mixed dark matter models, focusing on radial density profiles, velocity spectra and soliton formation in collapsed halos. We find that the effective granule masses decrease in proportion to the fraction of fuzzy dark matter which quadratically suppresses soliton growth, and that a central soliton only forms if the fuzzy dark matter fraction is greater than 10%. The Nyx framework supports baryonic physics and key astrophysical processes such as star formation. Consequently, AxioNyx will enable increasingly realistic studies of fuzzy dark matter astrophysics.

Ultra-light axions and the kinetic Sunyaev-Zel'dovich Effect

“…[202] for massive neutrinos, and account for the fact that some fraction of the ULA mass density will be bound and some will be unbound. Given the tremendous recent progress in numerical simulations of ULA structure formation using hydrodynamic, Schrödinger-Poisson, and modified N -body solvers [94,[203][204][205], it would be interesting to directly apply simulation outputs (including baryon physics where possible) in order to more realistically model kSZ observables in the presence of ULAs.…”

Probing non-thermal light DM with structure formation and $N_\mathrm{eff}$

“…Of particular interest with respect to above mentioned questions are DM mixtures of cold and warm DM species. Often, the cold component is considered to be of standard ΛCDM origin, while the warm component is made of something else: popular extensions involve sterile neutrinos [12][13][14], ultralight particles [15,16], axions [17], fuzzy DM [18,19] or non-cold thermal relics [20,21]. Some of the first models invoked neutrinos as a hot DM candidate mixed with a cold component (see for instance [22][23][24][25][26]).…”

Nonlinear cosmological structure with ultralight bosons via modified gravity

“…So far, the cosmological evolution is well understood up to the level of linear perturbations, with even dedicated versions of the leading Boltzmann codes that allow a precise comparison of the model with a full suite of cosmological observations [15][16][17][18]. However, the nonlinear formation of structure still is a difficult task, and it has been until recently that full simulations seem to be at hand for a proper study of the formation of structure under axion models [19][20][21][22][23]. Although this will allow the systematic testing of the model in the near future, it is necessary to find options for the generation of rapid cosmological simulations much in the same way as it has been done for Cold Dark Matter (CDM) and Modified Gravity models [24][25][26][27].…”