Fuzzy dark matter halos with repulsive self-interactions: coherent soliton and halo vortex network with moderate self-coupling

TL;DR

This study investigates how moderate repulsive self-interactions influence fuzzy dark matter halos, revealing larger cores with lower density and altered vortex structures, while outer regions remain quantum-pressure supported.

Contribution

It provides new insights into the effects of self-interactions on fuzzy dark matter halos, especially on core size, vortex networks, and coherence properties, bridging quantum and classical regimes.

Findings

Cores grow larger and less dense with increasing self-coupling.

Vortex network length remains stable over simulation timescales.

Coherence measures distinguish the condensed core from the quasi-coherent halo.

Abstract

We examine the impact of moderate repulsive self-interactions on fuzzy dark matter halos generated by merging smaller Gaussian density concentrations. We study the size of the core and the granules, the spatial dependence of the field's coherence, the turbulent vortex tangle and the oscillation frequency of the central soliton, covering the range from quantum-pressure-dominated to self-interaction-dominated stabilisation of the solitonic core. For the probed self-coupling strengths $g$ and with a fixed initial configuration, mergers with increasing $g$ result in cores with increased size and a reduced central density, oscillating with decreased frequency, in accordance with expectations from the study of isolated Self-interacting Fuzzy Dark Matter (SFDM) solitons. By contrast, the characteristic granule size and typical inter-vortex distances in the surrounding halo are only mildly affected, growing much less relative to the core. The total length of the vortex network, although less robust, shows no signs of decay over our simulation timescales. The generated halos therefore develop central self-interaction-dominated cores, but with the outer halos still supported by quantum-pressure and classical kinetic energy in equipartition as in the non-interacting case. Furthermore, measures of coherence of the field clearly separate the condensed core, identified via the Penrose-Onsager (largest eigenvalue) mode of the entire classical field, from the surrounding quasi-coherent halo. Unlike the $g=0$ case, we observe a relative increase of incoherent fluctuations coexisting with the coherent mode at the centre of the halo with increasing $g$, a phenomenon also observed in laboratory condensates at non-zero temperature.