Through the Looking Glass into the Dark Dimension: Searching for Bulk Black Hole Dark Matter with Microlensing of X-ray Pulsars

TL;DR

This paper proposes using X-ray microlensing of distant pulsars to detect or constrain primordial black holes in a five-dimensional dark universe, potentially accounting for all dark matter in a mass range inaccessible to Hawking radiation constraints.

Contribution

It introduces a novel method of searching for 5D primordial black holes via X-ray microlensing, extending the mass range beyond traditional 4D constraints.

Findings

Future X-ray microlensing can probe PBHs in the mass range $10^{16.5}$ to $10^{17.5}$ grams.

5D PBHs could constitute all dark matter within certain mass ranges.

The method can test dark matter scenarios that evade Hawking radiation constraints.

Abstract

Primordial black holes (PBHs) hidden in the incredible bulk of the dark dimension could escape constraints from non-observation of their Hawking radiation. Since these five-dimensional (5D) PBHs are bigger, colder, and longer-lived than usual 4D PBHs of the same mass $M$, they could make all cosmological dark matter if $10^{11} \lesssim M/{\rm g} \lesssim 10^{21}$, i.e., extending the 4D allowed region far down the asteroid-mass window. We show that these evasive PBHs could be search for by measuring their $X$-ray microlensing events from faraway pulsars. We also show that future $X$-ray microlensing experiments will be able to probe the interesting range ($10^{16.5} \lesssim M/{\rm g} \lesssim 10^{17.5}~{\rm g}$) where an all dark matter interpretation in terms of 4D Schwarzschild PBHs is excluded by the non-observation of their Hawking radiation.