# Using PySiUltraLight to Model Scalar Dark Matter with Self-Interactions

Academic Article

### Abstract

• We introduce PySiUltraLight, a modification of the PyUltraLight code that includes self-interaction terms to model the dynamical evolution of axion fields. PyUltraLight simulates ultralight dark matter dynamics. We will use a boson mass of $10^{-22} \mathrm{eV}/\mathrm{c}^2$ in this paper. We use PySiUltraLight to produce collapsing solitons, spatially oscillating solitons, and exploding solitons which prior analytic work shows will occur with attractive self-interactions. We test the maximum mass criteria described in arXiv:1604.05904 for a soliton to collapse when attractive self-interactions are included. Implementing an approximate Gaussian ansatz for the wave function of the solitons, we calculate the oscillation frequency as a function of soliton mass and equilibrium radius in the presence of attractive self-interactions. We verify our code and that when the soliton mass is below the critical mass ($M_c = \frac{\sqrt{3}}{2}M_{\mathrm{max}}$) described in arXiv:1604.05904 and the initial radius is within a specific range, solitons are unstable and explode. We also analyze both binary soliton collisions and a soliton rotating around a central mass with attractive and repulsive self-interactions. We find that when attractive self-interactions are included, the density profiles get distorted after a binary collision. We also find that a soliton is less susceptible to tidal stripping when attractive self-interactions are included. We find that the opposite is true for repulsive self-interactions in that solitons would be more easily tidally stripped.

• astro-ph.CO
• hep-ph