Cosmological structure formation and soliton phase transition in fuzzy dark matter with axion self-interactions

We investigate cosmological structure formation in fuzzy dark matter (FDM) with the attractive self-interaction (SI) with numerical simulations. Such a SI would arise if the FDM boson were an ultra-light axion, which has a strong CP symmetry-breaking scale (decay constant). Although weak, the attractive SI may be strong enough to counteract the quantum 'pressure' and alter structure formation. We find in our simulations that the SI can enhance small-scale structure formation, and soliton cores above a critical mass undergo a phase transition, transforming from dilute to dense solitons.

Automated summary

We investigate cosmological structure formation in fuzzy dark matter (FDM) with attractive self-interaction using numerical simulations. The attractive self-interaction arises if the FDM boson is an ultra-light axion with a strong CP symmetry-breaking scale. Despite its weakness, the attractive self-interaction can counteract quantum pressure and modify structure formation. Our simulations show that the self-interaction enhances small-scale structure formation and soliton cores undergo a phase transition from dilute to dense solitons above a critical mass.