Clustering of JWST LRDs. Implications for PBHs and other early-forming seeds

Gert Hütsi

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arXiv · 2610.23806

Clustering of JWST LRDs. Implications for PBHs and other early-forming seeds

Gert Hütsi

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Abstract

We use the observed abundance and spatial clustering of JWST little red dots (LRDs) over z = 4--8 to confront two formation scenarios: the standard picture in which LRDs form in virialized dark-matter halos, and one in which they are seeded by a dynamically subdominant population of primordial black holes (PBHs). The halo formation scenario accounts for both observables naturally and without fine-tuning. In the PBH scenario, matching the observed LRD abundance requires a negligibly small PBH mass fraction, and a power-spectrum analysis shows that such a Poisson isocurvature component predicts a clustering signal far below what is observed. The same conclusion holds for any population of dynamically subdominant early-forming seeds, unless their initial clustering is finely tuned or their activity is tied to massive host halos. We conclude that the spatial clustering of JWST LRDs strongly favours the standard halo formation picture and disfavours PBHs, or similar early-forming seeds, as a randomly activated LRD population; PBHs remain viable as seeds only if their activity is governed by massive host halos, in which case clustering alone cannot distinguish them from astrophysical seeds.

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Gert Hütsi. 2026-10-16. Clustering of JWST LRDs. Implications for PBHs and other early-forming seeds. https://arxiv.org/abs/2610.23806

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