Quantum Scales of Galaxies from Self-interacting Ultralight Dark Matter

Abstract: We derive the characteristic scales for physical quantities of galaxies, such as mass, size, acceleration, and angular momentum, within the self-interacting ultralight dark matter (ULDM) model. Due to the small mass of ULDM, even minor self-interactions can drastically alter these scales in the Thomas-Fermi limit. Even in this limit, the characteristic mass can be determined by quantum pressure rather than by repulsive forces. We suggest that these characteristic scales are connected to certain mysteries of observed galaxies such as the universal acceleration scale or the constant surface density of galaxies. Oscillation of ULDM field can explain the current cosmological density of dark matter. Many cosmological constraints imply the energy scale $\tilde{m}$ of order of $10~eV$ and a GUT scale phase transition related to ULDM.