upgradeFDM · Upgrading the Fuzzy Dark Matter Model

Upgrading the Fuzzy Dark Matter Model

The project is aiming to investigate exotic characters and properties of the populated dark matter candidate with ultralight mass, called fuzzy dark matter (FDM) or Bose-Einstein-condensate (BEC) dark matter, by incorporating new ingredients, a self interaction and thermal/incoherent component, and investigate the role of quantized vortices on the dark matter (DM) halo structures with the FDM wavy nature via numerical simulations. It would upgrade our understanding of DM and the results will help further dark matter search. Our extensive investigations guide us to our first publication, “Coherent and incoherent structures in fuzzy dark matter halos” [DOI: 10.1093/mnras/stad591], bringing several new insights into FDM halos. To understand the primary properties of the FDM field, we first investigate the coherent properties of FDM via 'galaxy collision' numerical experiments and integrate the concept of the classical-field method from atomic BECs, the fellow's original discipline. We find out that the core of a halo is fully coherent but is surrounded by a highly incoherent field and such a coherent-incoherent crossover can surprisingly be captured by a bimodal core-halo profile, matching the solitonic core profile in FDM and the cold DM profile in the outer region. This bimodal profile can be further used to describe the dynamical halos and the extracted core length scale is anti-correlated to the peak location of the power spectrum of the whole FDM density field. This indicates that the oscillation of the core can be probed by the observational power spectrum. We also identify the source of fluctuations leading to the decoherence at the outer region of FDM halos by looking at the energy distributions. The core area is dominated by the quantum pressure, against the gravitational collapse. In the outer region, we found that quantum pressure energy is comparable with the classical kinetic energy (while there is a quantum component in the FDM) consisting of the sound-like and rotational components, and the latter plays a crucial role. This suggests that vortices are the source of fluctuations, and our unique visualization shows that there are large amounts of quantized vortices in the outer hallos (see the attached figure) and the FDM halos are actually in a turbulent state. In addition, we notice that the characteristic size of granules (local density lumps in the outer halo) is associated with the intervortex distance from the granule and vortex energy spectra. We have applied the methods/concepts in atomic BEC studies and brought new insights into the FDM halo profiles, showing the highly excited halos are not just density fluctuations from the waviness effects. It builds up the benchmark with great high-quality scientific results and paves the way for our exploration of the role of self interaction and additional incoherent component from the dark matter particles. Apart from the current published work, we are preparing further publications on the role of self-interaction and the core oscillation from the semi-analytical and quasi-particle approaches, rather than the perspective of a single-particle excited state considered in the existing literature. This project has been very successful in both the extraordinary scientific finding and the fellow’s career development.

Data: CORDIS, © European Union