Could regular primordial black holes be dark matter?

Abstract

The recent proposal proposed by Paul Davies and colleagues [Phys. Rev. D \textbf{111} (2025) no.10, 103512] that regular primordial black holes (RPBHs) form stable, zero-temperature remnants and could thereby constitute dark matter is critically examined. While the introduction of a fundamental length scale indeed regulates the Hawking temperature, preventing its divergence, we show that the evaporation timescale for such RPBHs is infinite. This result holds generically for analytic regular black hole spacetimes under standard adiabatic and quasi-static evolution. Consequently, RPBHs never actually reach a true remnant state within any finite time, but instead persist as slowly evaporating objects with a non-zero luminosity. When the combined emission from a cosmological population of these near-remnants is considered, the resulting radiation is found to violate stringent observational constraints from the cosmic microwave background and extragalactic gamma-ray backgrounds. Therefore, low-mass RPBHs are not viable dark matter candidates.