Do primordial black holes exist

[wolram]

A PBH is a hypothetical type of black hole that is formed not by the gravitational collapse of a large star but by the extreme density of matter present during the universe's early expansion.

It has been proposed that dark mater is made up of primordial black holes. One theory proposes that they are in the mass range of 1017 g to 1026 g, based on the expectation that at this low mass they would behave as expected of other particle candidates for dark matter. They would be within the typical mass range of asteroids. Another theory is that dark matter consists of larger black holes, about 30 times the mass of the sun (about 6 × 1034 g).
One way to detect primordial black holes is by Hawking radiation, if they are small enough to radiate, and if Hawking radiation exists, otherwise they will be extremely difficult to detect.

 

[phinds]

Have you tried a forum search? There have been numerous discussions of this.

 

[Chronos]

A recent summary of observational constraints on PBH abundance is discussed here; https://arxiv.org/abs/1607.06077, Primordial Black Holes as Dark Matter. The more reliable constraints are deduced from the diffuse gamma ray background and micro lensing surveys. These tend only to rule out the possibility that PBH's can significantly contribute to the DM inventory, not their existence in general. While gamma ray background constraints are vulnerable to the unproven assumption we have correctly quantified contributions due to Hawking radiation, it is considered well founded in theory. Microlensing constraints are more robust. It is virtually unreasonable to suspect any dubious assumptions might affect lensing surveys. There is also supporting evidence in forms including BBN [big bang nucleosynthesis], CMB and dynamical constraints. The long and short of it is current evidence for PBH's as a dominant contributor to the DM budget is, at best, inconclusive