Small-scale structure in vector dark matter

TL;DR

This study uses 3+1D simulations to compare small-scale structures of vector and scalar dark matter, revealing key differences in core properties, interference patterns, and angular momentum that could help distinguish them observationally.

Contribution

It provides the first detailed simulation-based comparison of vector and scalar dark matter small-scale structures, highlighting observable differences.

Findings

VDM has less wave interference than SDM.

Core-to-halo mass ratio is lower in VDM.

Positive correlation between total spin and core spin in VDM.

Abstract

We investigate the differences in the small-scale structure of vector dark matter (VDM) and scalar dark matter (SDM) using 3+1 dimensional simulations of single/multicomponent Schr\"{o}dinger-Poisson system. We find that the amount of wave interference, core-to-halo mass ratio (and its scatter), spin of the core, as well as the shape of the central regions of dark matter halos can distinguish VDM and SDM. Starting with a collection of idealized halos (self-gravitating solitons) as an initial condition, we show that the system dynamically evolves to an approximately spherically symmetric configuration that has a core surrounded by a halo of interference patterns in the mass density. In the vector case, the central soliton in less dense and has a smoother transition to an $r^{-3}$ tail compared to the scalar case. As compared to SDM, wave interference in VDM is $\sim 1/\sqrt{3}$ times smaller, resulting in fewer low and high density regions, and more diffuse granules in the halo. The ratio of VDM core mass to the total halo mass is lower than that in SDM, with a steeper dependence on the total energy of the system and a slightly larger scatter. Finally, we also initiate a study of the evolution of intrinsic spin angular momentum in the VDM case. We see a positive correlation between the total intrinsic spin in the simulation and the spin of the final central core, with significant scatter. We see large intrinsic spin in the core being possible even with vanishing amounts total angular momentum in the initial conditions (at least instantaneously). Our results point towards the possibility of distinguishing VDM from SDM using astrophysical and terrestrial observations.