Observing Micro Black Hole Dark Matter

Abstract

Primordial micro black holes can constitute dark matter if short-distance gravity is modified by extra dimensions or a large number of species and if the memory-burden effect sufficiently suppresses Hawking evaporation. The resulting black holes in the transition regime differ from their four-dimensional Einsteinian counterparts through their mass--radius relation, temperature, entropy, and lifetime, which can render even very light objects cosmologically stable. The most promising observational consequences of such micro black holes dark matter are analysed. Neutron star survival yields the most robust constraints, while a narrow region of parameter space can simultaneously remain viable and address the missing-pulsar problem in the Galactic center. Diffuse evaporation signals in neutrino telescopes are found to be relevant mainly in extra-dimensional scenarios, whereas in generic species models, visible emission is strongly suppressed by evaporation into dark sectors. Merger-induced evaporation bursts can provide an additional probe in extra-dimensional realisations if the post-merger remnant briefly returns to the semiclassical phase. Overall, micro black holes dark matter remains phenomenologically viable in constrained regions, with neutron stars, neutrino telescopes, and merger signatures providing complementary tests.

Figures (5)

• Figure 1: The panels show the $M$--$M_{\mathrm{f}}$ plane for different values of $n$ and $k = 1$ for the extra-dimensional case. The orange shaded region is excluded by neutron star existence, the red region is the evaporation bound, the ice-blue-shaded shaded region is the potential bound set by IceCube assuming a sensitivity that requires a signal of one event per year since operation start. The black shaded region shows the area of the parameter space where the size of the black holes exceeds the compactification radius $R$ and is therefore no $\mu$BH anymore.
• Figure 2: Same as Fig. \ref{['fig:1']}, but for $k = 2$.
• Figure 3: The panels show the $M$--$M_{\mathrm{f}}$ plane for different values of $n$ and $k$ for the species case. The colour coding is as in Figs. \ref{['fig:1']} and \ref{['fig:2']}. Here, the black shaded region shows the area of the parameter space where the size of the black holes exceeds $\sqrt[\ ]{N}\space M_{\mathrm{P}}$ and is therefore no $\mu$BH anymore.
• Figure 4: The panels show the $M$--$M_{\mathrm{f}}$ plane for different values of $n$ and $k = 2$ for the extra-dimensional case if one aims for a solution for the missing-pulsar problem. The orange shaded region is excluded by neutron star existence, meanwhile the yellow region is excluded as it would allow neutron stars being stable in the center of the Milky Way. The red region is the evaporation bound, the ice-blue-shaded region is the potential bound set by IceCube assuming a sensitivity that requires a signal of one event per year since operation start. The black shaded region shows the area of the parameter space where the size of the black holes exceeds the compactification radius $R$ and is therefore no $\mu$BH anymore. The green shaded region is where neutron stars are stable.
• Figure 5: The flux of evaporated neutrinos on the Earth for different scenarios of extra-dimensional theories. Two scales for $M_{\mathrm{f}}$ are investigated, motivated by Refs. Arkani-Hamed:1998jmvMontero:2022prj. The mass of the black holes has been chosen to be the lightest value allowed for such a scenario as they lead to the highest flux. The red dots show the bound on neutrinos which have the energies of the evaporated neutrinos. The orange dots show the flux in case half of the black hole evaporates before it reenters the memory burden phase. The blue dots show the same in case just a fraction of $1/\sqrt[\ ]{S}$ evaporates. The bounds of the fluxes are stemming from Refs. Super-Kamiokande:2015qekANTARES:2024ihw.