Description
The Hawking evaporation of primordial black holes (PBHs) induces local reheating of the Universe, generating transient hot spots that persist over their evaporation timescale. Within this framework, we develop a method to compute the decay rate of metastable vacua in cosmological settings, circumventing conceptual issues associated with the Hartle–Hawking and Unruh vacua. Applying our approach to the electroweak vacuum instability, we derive constraints on the PBH abundance from the condition that if the electroweak vacuum is metastable, then a large population of evaporating PBHs is ruled out.
