Predictions on the abundance of primordial black holes: results from the SMILE VLBI milli-lensing sample
Abstract
Primordial black holes (PBHs) formed in the early universe represent a well-motivated dark matter candidate. However, their abundance in the intermediate-to-high mass range (106-109 M⊙) remains relatively less constrained. In this mass regime, the corresponding Einstein radii on the milliarcsecond scale make Very Long Baseline Interferometry (VLBI) the most direct observational probe via milli-lensing of compact radio sources. In this paper, we present predictions for the abundance of PBH dark matter (fPBH) using the large SMILE sample of ∼ 5000 flat-spectrum compact radio sources. Under the optimistic observational conditions (with an angular resolution of 1.5 mas, a maximum image separation of 100 mas, and a maximum detectable flux ratio of $40$), assuming that no milli-lensing events are confirmed, we obtain the projected 95% upper limit of fPBH≲0.12% in the intermediate-to-high mass range, which would be approximately an order of magnitude tighter than previous VLBI milli-lensing limits. Broader lognormal mass functions yield correspondingly weaker projected limits. Generalising the optical depth to account for magnification bias and finite-core resolvability changes these projected limits by only about $5$%. Moreover, we show that the predicted limits are highly sensitive to a small number of confirmed events, i.e., even one confirmed milli-lensing event would relax the projected upper limit to $0.20$%, highlighting the critical importance of robust candidate confirmation in the SMILE sample. Finally, under the optimistic baryonic accretion scenario, the PBH mass growth changes the projected limits by ≲ 1% within the VLBI-sensitive mass range, confirming the robustness of our results.
Related
- 2% determination of N eff from primordial element abundance, cosmic microwave background, and baryon acoustic oscillation measurements
- Localized Enhancements of the Primordial Power Spectrum and the Abundance of Early Bright Galaxies
- Fast Lensing And Sub-minute High-accuracy photometry (FLASH) with JWST: Pipeline and Primordial Black Hole Microlensing Constraints from M31
- Detection of cosmic strings by gravitational wave lensing. Predictions for Einstein Telescope
- Probing the Seed Effect of Supermassive Primordial Black Holes with Weak Gravitational Lensing
BibTeX
@misc{jiang2026predictions,
title = {{Predictions on the abundance of primordial black holes: results from the SMILE VLBI milli-lensing sample}},
author = {Xinyue Jiang and Shuo Cao and Marek Biesiada and Xuanni Chen and Yalong Nan and Xinyang Jin and Xuchen Tai},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.20329},
eprint = {2609.20329},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.20329},
}
RIS
TY - UNPB
TI - Predictions on the abundance of primordial black holes: results from the SMILE VLBI milli-lensing sample
AU - Xinyue Jiang
AU - Shuo Cao
AU - Marek Biesiada
AU - Xuanni Chen
AU - Yalong Nan
AU - Xinyang Jin
AU - Xuchen Tai
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.20329
UR - https://arxiv.org/abs/2609.20329
AB - Primordial black holes (PBHs) formed in the early universe represent a well-motivated dark matter candidate. However, their abundance in the intermediate-to-high mass range (10^6-10^9 M_⊙) remains relatively less constrained. In this mass regime, the corresponding Einstein radii on the milliarcsecond scale make Very Long Baseline Interferometry (VLBI) the most direct observational probe via milli-lensing of compact radio sources. In this paper, we present predictions for the abundance of PBH dark matter (f_PBH) using the large SMILE sample of ∼ 5000 flat-spectrum compact radio sources. Under the optimistic observational conditions (with an angular resolution of 1.5 mas, a maximum image separation of 100 mas, and a maximum detectable flux ratio of $40$), assuming that no milli-lensing events are confirmed, we obtain the projected 95% upper limit of f_PBH≲0.12% in the intermediate-to-high mass range, which would be approximately an order of magnitude tighter than previous VLBI milli-lensing limits. Broader lognormal mass functions yield correspondingly weaker projected limits. Generalising the optical depth to account for magnification bias and finite-core resolvability changes these projected limits by only about $5$%. Moreover, we show that the predicted limits are highly sensitive to a small number of confirmed events, i.e., even one confirmed milli-lensing event would relax the projected upper limit to $0.20$%, highlighting the critical importance of robust candidate confirmation in the SMILE sample. Finally, under the optimistic baryonic accretion scenario, the PBH mass growth changes the projected limits by ≲ 1% within the VLBI-sensitive mass range, confirming the robustness of our results.
ER -