Evolution of perturbations and spectra in multi-component ultralight axionic universes
Yi-Hsiung Hsu1*, Tzihong Chiueh1,2,3
1Institute of Astrophysics, National Taiwan University, Taipei, Taiwan
2Department of Physics, National Taiwan University, Taipei, Taiwan
3Center for Theoretical Physics, National Taiwan University, Taipei, Taiwan
* Presenter:Yi-Hsiung Hsu, email:arthurhsu3388@gmail.com
The spectra for multi-component ultralight axion dark matter universes are computed and analyzed. To achieve power spectra, evaluating the evolution of axions for each wavenumber k mode is required. Due to the stiff Klein-Gordon equation and strong Thomson scattering, this computation is formidable. Our program applies the Schrödinger equation and diffusion approximation, which reduces real-time from about 30 minutes to about 1 second while integrating the same interval and retaining the accuracy higher than 95%. This improved scheme enables the construction of initial conditions for the future generation of simulations. In the two-component universe, we evaluate different configurations among cold dark matter, free particle axions, and extreme axions with different particle masses. With equal background energy for two components, it generally shows a less drastic spectral cutoff for the larger mass difference.

Keywords: Dark Matter, Multi-component Universe, Power Spectra