Small-Scale Clustering of Primordial Black Holes: The Little Red Dot Mass Function and the High-Redshift Galaxy Tension

Supermassive black holes (SMBHs) in “little red dots” (LRDs) discovered the James Webb Space Telescope (JWST) may result from runaway mergers of primordial black holes (PBHs) in clusters—through long–short mode coupling on small scales in the early Universe. In this framework, we derive the SMBH mass function, together with the compactness and overmassive features of LRDs. We also estimate that the dense gas residing in PBH clusters is consistent with LRD observations. In addition, SMBHs formed from PBH clusters can help accelerate galaxy formation at high redshifts, thus alleviating tension with $\mathrm{\Lambda }$CDM cosmology.