Abstract
We investigate the effects of producing dark matter by Hawking evaporation of primordial black holes (PBHs) in scenarios that may have a second well-motivated dark matter production mechanism, such as freeze-out, freeze-in, or gravitational production. We show that the interplay between PBHs and the alternative sources of dark matter can give rise to model-independent modifications to the required dark matter abundance from each production mechanism, which in turn affect the prospects for dark matter detection. In particular, we demonstrate that for the freeze-out mechanism, accounting for evaporation of PBHs after freeze-out demands a larger annihilation cross section of dark matter particles than its canonical value for a thermal dark matter. For mechanisms lacking thermalization due to a feeble coupling to the thermal bath, we show that the PBH contribution to the dark matter abundance leads to the requirement of an even feebler coupling. Moreover, we show that when a large initial abundance of PBHs causes an early matter-dominated epoch, PBH evaporation alone cannot explain the whole abundance of dark matter today. In this case, an additional production mechanism is required, in contrast to the case when PBHs are formed and evaporate during a radiation-dominated epoch.
Highlights
The nature and origin of dark matter still remain some of the main unresolved issues in particle physics, astrophysics, and cosmology
If all the dark matter in the universe is explained by dark matter produced in primordial black holes (PBHs) evaporation, one can express the upper limit on the initial abundance β of PBHs as a function of their mass MBH and the mass mχ of the dark matter particles by equating the dark matter abundance produced by PBH evaporation ΩBχ H to the observed dark matter abundance Ωc, FIG. 1
In this paper we have explored the effects of PBH evaporation, as a novel dark matter production mechanism, on well-motivated particle dark matter scenarios, including freeze-out, freeze-in, and gravitational production of dark matter
Summary
The nature and origin of dark matter still remain some of the main unresolved issues in particle physics, astrophysics, and cosmology. One intriguing dark matter production mechanism is the Hawking evaporation of a population of primordial black holes (PBHs). Very weakly interacting dark matter particles that come from PBHs cannot thermalize, and contribute directly to the dark matter abundance today In this case, the relevant production mechanisms, such as freeze-in or gravitational production of superheavy dark matter, must be reduced to produce less dark matter. Æ ð3Þ (þ for fermion emission and − for boson emission), where uiðE; tÞ is the total radiated energy per unit area, gi counts the number of degrees of freedom of the ith species, E is the energy of the emitted particle, and TBH is the horizon temperature of the black hole,.
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