Warm and Fuzzy Dark Matter: Free Streaming of Wave Dark Matter

Understand

Wave or fuzzy dark matter that is produced with relativistic wavenumbers exhibits free streaming effects analogous to warm or hot particle dark matter with relativistic momenta.

• Axions produced after inflation provide such a warm or mildly relativistic candidate, where the enhanced suppression and observational bounds are only moderately stronger than that from wave propagation of initially cold axions.
• More generally, the free streaming damping also impacts isocurvature fluctuations from generation in causally disconnected patches.
• As coherent spatial fluctuations free stream away they leave incoherent and transient superpositions in their wakes.