Constraining ultra-light axions with galaxy cluster number counts

In this paper we investigate the potential of current and upcoming cosmological surveys to constrain mass abundance ultra-light axion (ULA) cosmologies with galaxy cluster number counts. ULAs, sometimes also referred as Fuzzy Dark Matter, are well-motivated in many theories beyond Standard Model could potentially solve $\Lambda$CDM small-scale crisis. Galaxy counts provide a robust probe formation structures Universe. Their distribution redshift is strongly sensitive underlying linear matter perturbations. forecast explore two scenarios, firstly an exclusion limit on given no-axion model secondly constraints model. With obtain lower limits ULA order $m_a \gtrsim 10^{-24}$ eV. However, result depends heavily smallest reliably observable clusters for survey. Cluster counts, like other probes, display approximate degeneracy vs. parameter space, which dependent characteristics probe. These degeneracies different probes. Hence might complementary window properties axions.