Kavli Affiliate: Risa Wechsler
| Summary:
We generalize lower limits on the dark matter (DM) particle mass $m$ derived from Milky Way (MW) satellite galaxy abundances to scenarios in which DM is an ultralight scalar field produced with a field power spectrum peaked at a subhorizon wavenumber $k_*$. In these models, the DM field free-streams similarly to warm DM while also exhibiting significant small-scale wave interference effects. The resulting dimensionless density power spectrum shows two effects: (i) free-streaming suppression at $k_rm fssim k_rm eq/[(k_*/a_rm eqm)ln(a_rm eqm/k_*)]$; (ii) Poisson-like enhancement related to wave interference at $kgtrsim10^-2k_*$, which saturates near the Jeans scale $k_rm Jsim k_rm eq/(k_*/a_rm eqm)$. Comparing these predictions with established constraints on a free-streaming cutoff in the linear matter power spectrum from the MW satellite population and assuming that warm ultralight DM does not change the form of the galaxy–halo connection relative to cold DM, we obtain $m>6times10^-18,rm eV,(k_*/10^4,rm Mpc^-1)$ for $k_*>10^4,rm Mpc^-1$ at 95% confidence. For smaller $k_*$, Poisson-noise enhancement on MW satellite scales weakens the constraint, yielding $m>6times10^-18,rm eV,(k_*/10^4,rm Mpc^-1)^2$ for $k_*<10^4,rm Mpc^-1$ at 95% confidence.
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