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Ufuk Aydemir
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Dark matter and baryogenesis from not quite black holes
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It is now certain that there are extremely
dark and compact  objects that are so far
consistent with black holes (BH) in GR. However,
the current observations cannot accurately
probe near-horizon physics, and it is indeed
this regime where deviations from GR, possibly
towards quantum gravity, might first manifest.
Such deviations are strongly motivated by
the information loss problem. One possibility
is that quantum gravity prevents formation
of event horizon, generating horizonless
ultra-compact objects (HUCOs) instead of
BHs. These objects would appear similar to
BHs for current experiments, but they could
leave distinctive imprints in gravitational
wave signals as echoes, and as far as the
current observations are concerned, they
remain in the picture. Since existence of
such an object would directly point to a
theory beyond GR, it is important to study
their phenomenology.

In this talk, I will discuss phenomenology
of such an object, namely 2-2-hole, which
arises in quadratic gravity, a candidate
theory for quantum gravity. A 2-2-hole possesses
essentially the exterior of a BH without
a horizon and hence, as a probable endpoint
of gravitational collapse, it provides a
resolution to the information loss problem.
When sourced by thermal gas, a 2-2-hole at
relatively early stages of its evaporation
imitates the thermodynamic characteristics
of a BH. At late stages, the evaporation
essentially stops,  leading to a stable remnant.
Primordial 2-2-hole remnants, in comparison
and contrast to the PBH remnants, constitute
DM candidates. Alternatively, the particle
DM scenario can also be realized, where the
majority of DM consists of particles produced
by the evaporation of primordial 2-2-holes,
and the remnant contribution is secondary.
Moreover, 2-2-hole evaporation in the early
universe can produce particles that are responsible
for the baryon asymmetry, in which case baryogenesis
through direct B-violating decays or through
leptogenesis can both be realized.


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