The fast, the slow and the merging: probes of evaporating memory burdened PBHs

TL;DR

This paper explores how the memory-burden effect in evaporating primordial black holes creates new dark matter windows, predicts observable astrophysical signals, and constrains theoretical models through cosmological and astrophysical data.

Contribution

It introduces the memory-burden effect as a key factor in PBH evolution, opening new mass windows for dark matter and providing observational constraints.

Findings

Memory-burden effect stabilizes PBHs, creating new dark matter windows.

Mergers produce observable high-energy particle fluxes.

Cosmological data constrains the critical exponent of the memory-burden phenomenon.

Abstract

The so-called memory-burden effect implies that evaporating Primordial Black Holes (PBHs) inevitably stabilize before complete decay. This stabilization opens a new mass window for PBH Dark Matter below $10^{15}\,$g. The transition to the memory-burdened phase is not instantaneous but unfolds over cosmological timescales, with some PBHs entering this phase in the present epoch. Additionally, a fraction of PBHs undergo mergers today, forming ''young'' semiclassical black holes that evaporate at unsuppressed rates. Both processes generate fluxes of stable astrophysical particles, which are constrained by current measurements of high-energy $\gamma$-rays and neutrinos. Moreover, the steep increase in energy injection at higher redshifts perturbs the ionization history of the Universe, leading to complementary bounds from observations of the CMB temperature and polarization anisotropies. We find that the reopened window enabled by the memory-burden effect is largely within reach of detection, both locally and across cosmological distances. We further describe how our findings restrict the values of the critical exponent characterizing the memory burden phenomenon.