On the Possibility of Probing Early Matter Domination with Primordial Black Holes
Sammanfattning: Primordial black holes (PBHs) are expected to form in the very early universe, and therefore, we could use them to probe preBBN times. Astrophysical observations permit the placement of bounds on the abundance of PBHs. Combining these bounds with predictions of PBH formation and the resulting PBH abundances, we explore the possibility to constrain an epoch of early matter domination (MD). For this analysis, we incorporate the recently obtained and most stringent bounds on PBHs from 21 cm observations. We assume density perturbations described by a nearpowerlaw form of the curvature power spectrum consistent with the Planck 2018 results and derive the corresponding PBH mass function using recent results from the literature. To place constraints on an early matterdominated (MD) epoch, we compare this with upto date bounds on PBHs, adding those from 21 cm astronomy, using a formalism to apply monochromatic constraints to extended mass functions. We find that 21 cm bounds on PBHs may probe early MD if it lasts for a duration of at least ∼ 12 efolds and ends at a reheating temperature T_min < T_reh ≲ 105.5 GeV, where Tmin depends on the duration of the MD, the spectral index ns, and αs. For optimistic assumptions, our derived limits on the spectral index ns extend into the Planck 2018 67% upper confidence region of n_s = 0.9649 ± 0.0042, nearly reaching its median n_s = 0.9649, if we neglect the running αs. Our bounds on the running α_s show that early MD is incompatible with positive running α_s ≳ 0.
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