Mixed Dark Matter Simulations Reveal Redshift-Dependent Halo Suppression That Could Finally Test Fuzzy Dark Matter Against Observations

The arXiv preprint from Johnston et al. (2026) uses AxiREPO simulations to show that even a 10-30% fuzzy dark matter fraction with particle mass 10^{-24.5} eV measurably alters the halo mass function, producing a systematic drop in low-mass halos that grows stronger at higher redshift. Their grid-based halo finder merges CDM particles and FDM wave density into a single field, revealing that FDM largely follows CDM on large scales while wave interference carves out small-scale power. This extends earlier pure-FDM work (Schive et al. 2014, ApJ) by demonstrating that partial mixing still yields observable suppression without the extreme core formation seen in 100% FDM models. The authors fit a phenomenological suppression function accurate to 0.1-0.2 dex across z=1-4, offering a practical bridge to semi-analytic galaxy formation codes. However, the study is limited to f ≤ 0.3 and does not yet confront Milky Way satellite counts or strong-lensing flux anomalies, both of which have historically favored CDM. A related analysis by Hui et al. (2017, PRD) predicted that mixed models could relieve the too-big-to-fail problem while preserving large-scale structure; the new simulations quantify exactly how much FDM fraction is needed at each epoch. Because this remains a preprint, independent groups must still verify the halo finder against full wave-function solvers before the results enter cosmological pipelines.