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Spatial distribution of DM and BAU induced by PBH hot spots

Characterize the spatial distribution of dark matter abundance and baryon/lepton asymmetry arising from evaporating primordial black hole hot spots due to the modified small-scale thermal evolution of the plasma, and ascertain whether such spatial variation leads to observable signals in cosmology.

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Background

Throughout the paper the authors model the local heating of the primordial plasma around evaporating primordial black holes (PBHs), which produces hot spots with non-uniform temperature profiles. For phenomenological applications (leptogenesis and thermal dark matter), they assume that after PBHs evaporate the plasma equilibrates and any particle abundances produced near hot spots become homogeneous.

In the conclusion, the authors explicitly note that this homogeneity assumption may be inadequate: the modified thermal evolution on small scales caused by PBH hot spots could imprint spatial variation in dark matter density or baryon/lepton asymmetry. They state that the detailed paper of this spatial distribution and its potential observables is left for future work.

References

In reality, the thermal history of the Universe is locally affected by the presence of PBH hot spots. Whereas the distance that separates PBHs from one another when they evaporate may be much smaller than the Hubble radius at that time, --- which is commonly used to argue that PBHs inject particles in a homogeneous way in cosmology --- this modified evolution of the thermal bath on small scales could lead to spatial variation in the DM abundance, or the baryon/lepton asymmetry of the Universe, leading to observable signals. We leave the details of such a spatial distribution for future work.

— Primordial Black Hole Hot Spots and Out-of-Equilibrium Dynamics (2409.02173 - Gunn et al., 3 Sep 2024) in Section 6 (Conclusion)