Speaker
Description
Primordial black holes (PBHs) provide a unique connection between early-Universe cosmology, gravity, and particle physics. Light PBHs evaporate through Hawking radiation, and those lighter than about a kiloton disappear before Big Bang nucleosynthesis. Nevertheless, their cosmological effects need not disappear with them. In this talk, I will discuss three examples of such persistent imprints, ranging from global and collective phenomena to local effects around individual PBHs. First, an abundant PBH population can induce an early matter-dominated era, during which fluctuations in the PBH distribution grow and overdense regions can collapse to form a new population of much heavier PBHs, potentially accompanied by a corresponding stochastic gravitational-wave background. Second, if PBHs are spatially biased and the particle composition of Hawking radiation differs from that of the background plasma, their evaporation can generate isocurvature perturbations, providing a way to constrain otherwise elusive light PBHs through CMB observations. Finally, Hawking particles can thermalize in the surrounding plasma and create local high-temperature hotspots. We show that cosmic expansion modifies their late-time cooling, with possible implications for local baryogenesis and dark-matter production. Together, these examples offer only a glimpse into the rich physics of PBHs.