Lower edge of the dark-matter window for 5D primordial black holes: an independent check with hard X-ray and soft gamma-ray data

In the dark-dimension scenario, light primordial black holes (PBHs) are five-dimensional (5D): colder and longer-lived than four-dimensional (4D) black holes of the same mass (arXiv:2506.14874). Earlier work estimated that 5D PBHs on the brane can make up all of the dark matter above about 10^14 g (arXiv:2206.07071) or 10^15 g (arXiv:2403.19604); the latter value follows from rescaling 4D gamma-ray limits at equal Hawking temperature. I compute the photon limits directly, with corrected BlackHawk v3.0 spectra, Galactic and extragalactic X-ray and gamma-ray data, and a conservative criterion (prediction below data plus 2 sigma in every bin). For a micrometre-size extra dimension (M_KK = 0.01-0.1 eV) the lower edge of the window lies at 1.3x10^13-3.5x10^13 g, and up to about 10^14 g if RXTE Galactic-ridge data are added. For the value of the 5D Planck scale used in the earlier work it lies at 1.0x10^16 g. The edge grows approximately as the square of the reduced 5D Planck mass. Published searches for PBH bursts are insensitive to 5D PBHs. Version 1 is the draft sent to the authors of arXiv:2206.07071, arXiv:2403.19604 and arXiv:2506.14874, and to the BlackHawk developers, on 13 October 2026. The calculations, code and text were prepared with the assistance of an AI system (Claude, Anthropic) under the direction of the author. A revised version with clarifications will follow; the results do not change.