Speaker
Description
We investigate the multiscale structure and dynamics of ultralight dark matter (ULDM) using a combination of spectral numerical methods and adaptive large-scale simulations within the Schrödinger–Poisson (SP) framework and its extensions. At small scales, we employ Fourier-based time-splitting techniques to resolve interference-driven dynamics and solitonic structure formation in scalar field dark matter. Within this framework, we first study the impact of self-interactions using three-dimensional Gross–Pitaevskii–Poisson simulations of soliton mergers. We find that repulsive interactions produce more extended, lower-density cores, while attractive interactions enhance central concentration and can trigger collapse above a critical mass threshold, systematically modifying core–halo relations.
We extend this analysis to generalized ULDM models with spin-0, spin-1, and spin-2 degrees of freedom, solving the SP system using spectral time evolution methods. Increasing spin leads to broader halo profiles with more pronounced envelope structures and significantly longer dynamical relaxation timescales. We further derive scaling relations that enable the construction of dynamically equivalent multi-soliton halos, providing an efficient route to explore parameter space without full re-simulations.
To connect these small-scale results to cosmological structure formation, we address the limitations of uniform-grid spectral methods and motivate the use of adaptive mesh refinement (AMR) techniques for large-scale evolution. In this context, we explore the applicability of grid-based codes such as GAMER for ULDM dynamics. To track halo evolution, we evolve a population of test particles coupled to the ULDM background potential and analyze their dynamics using standard halo-finding algorithms, allowing us to characterize dark matter distribution at large scales.