Primordial Black-Hole Mimicker in Quadratic Gravity as Dark Matter
  We discuss the astrophysical and cosmological implications of having
primordial thermal 2-2-hole remnants as dark matter. Thermal 2-2-holes emanate
in quadratic gravity as horizonless classical solutions for ultracompact
distributions of relativistic thermal gas. In contrast to a large 2-2-hole that
imitates the thermodynamic behaviour of a black hole, a small 2-2-hole at late
stages of evaporation behaves as a stable remnant with the mass approaching a
minimal value. These remnants as all dark matter can satisfy the corresponding
observational constraints provided that both the formation and remnant masses
are relatively small. The parameter space for the remnant mass is probed
through possible remnant mergers that would produce strong fluxes of
high-energy astrophysical particles; the high-energy photon and neutrino data
appear to favor towards the Planck-mass remnants, pointing to the
strong-coupling scenario for the quantum theory of quadratic gravity. The
formation mass, on the other hand, is constrained by the early-universe
cosmology, which turns out to require 2-2-holes to evolve into the remnant
state before Big Bang Nucleosynthesis.
