Impact of self-interaction and photon interactions on solitonic structures in ultralight dark matter

Abstract Ultralight dark matter (ULDM) has emerged as a compelling alternative to the standard cold dark matter (CDM) model by forming quantum-pressure-supported solitonic cores that address small-scale structure anomalies. In this work, we investigate the dynamics of solitons in ULDM by numerically evolving scalar field configurations under gravity, incorporating a range of interaction terms. We analyse soliton formation, stability, and collisions driven solely by quantum pressure and gravity, focusing first on the non-interacting case. We then introduce self-interactions via quartic, axion monodromy, logarithmic, and Sinh-Gordon potentials, each inducing distinct dynamical behaviour: repulsive quartic terms enhance stability, attractive interactions can lead to collapse, axion monodromy introduces saturation effects that modify core compactness, logarithmic terms suppress central density growth, and Sinh-Gordon interactions lead to deformation and fragmentation at high strengths. In order to analyse the effect of photon interactions beyond self-interactions, we observe the destabilization of solitonic structures even in the absence of scalar self-couplings. When both self- and photon-interactions are incorporated, soliton dynamics become highly sensitive to the specific potential, significantly influencing post-collision behaviour and long-term coherence. We provide a comprehensive analysis of soliton dynamics in ULDM across varying interaction types and parameter regimes, highlighting the complex dynamical behaviour of these quantum structures.