Updated constraints on primordial black hole evaporation

Abstract

The Hawking evaporation process, leading to the production of detectable particle species, constrains the abundance of light black holes, presumably of primordial origin. Here, we reconsider and correct constraints from soft gamma-ray observations, including of the gamma-ray line, at 511 keV, produced by electron-positron pair-annihilation, where positrons originate from black hole evaporation. First, we point out that the INTEGRAL detection of the Large Magellanic Cloud provides one of the strongest bounds attainable with present observations; and that future MeV gamma-ray telescopes, such as GECCO, will greatly enhance such constraints. Second, we discuss issues with previous limits from the isotropic flux at 511 keV and we provide updated, robust constraints from recent measurements of the diffuse Galactic soft gamma-ray emission and from the isotropic soft gamma-ray background.

Searching for Exploding black holes

“…The remainder of this paper is structured as follows: In the next section 2 we review the photon spectrum and light-curve of exploding PBH (note that other channels of PBH evaporation can be in principle used for detection, including notably cosmic rays [25,26], neutrinos [27], and gravitational waves [28,29]); the following section 3 discusses theoretical expectations for the density and rate of PBH explosions compatible with all other observational constraints, and presents a compact formula for the rate of explosions per unit volume per unit time today ṅPBH for a given generic initial PBH mass function ψ i , in the form ṅPBH = ρ DM ψ i (M U )/(3t U ), where M U ≃ 5.1 × 10 14 grams is the mass corresponding to a PBH with a lifetime equal to the age of the universe today, t U . Section 4 discusses the sensitivity estimate for a PBH at a given distance and time to complete evaporation for a number of observatories.…”

“…For masses above 10 14 grams, black hole evaporation is ongoing, and constrained by direct observation of the products of evaporation (cosmic rays and gamma rays); up to 10 17 grams, the strongest constraints are from evaporation to gamma-rays or to positrons (see e.g. the recent [26] that produced the strongest constraints from evaporation); in between 10 17 and 10 23 , PBH can be (but cannot exceed) the entirety of the cosmological cold dark matter; in the large range between 10 23 and 10 35 grams, the strongest constraints arise from microlensing surveys from different telescopes and observational strategies [34,35]; finally, around stellar masses, strong constraints arise from gravitational wave production [36], from the effects on the CMB of relativistic electrons produced by accretion on stellar-mass PBH [37], and from the stability of stellar clusters such as the one at the center of the Eridanus II dwarf galaxy [38]. For a summary of constraints, the Reader is directed to figure 4 and figure 10 of ref.…”

Effect of a high-precision semianalytical mass function on the merger rate of primordial black holes in dark matter halos

“…Primordial black holes (PBHs) are macroscopic candidates for dark matter. They are believed to form from small-scale, large-amplitude primordial density fluctuations during the early stages of the Universe (see, e.g., Villanueva-Domingo et al 2021;Green & Kavanagh 2021;Carr & Kuhnel 2021;Korwar & Profumo 2023). PBHs can have significant gravitational interactions that affect various cosmological observables.…”