Speaker
Description
Primordial black holes (PBHs) reshape how cosmic structure forms. I will trace how a PBH population's discreteness, dynamics, and formation history each leave their mark. Being discrete and massive, PBHs carry Poisson fluctuations that seed excess small-scale power and accelerate early structure growth. But PBHs also interact gravitationally with one another, and I will present the first cosmological simulations to fully resolve their few-body and relativistic dynamics. For example, many-body encounters give rise to a subcomponent of hot PBHs that suppresses structure up to billion-PBH scales, and these interactions also scramble binary merger times, reshaping the resulting gravitational-wave signal. I then turn to "warm" PBHs carrying a primordial velocity dispersion, for which we have built the first linear perturbation theory uniting discreteness with free streaming. Finally, I show that PBH formation is rarely clean: the same large primordial fluctuations produce a far greater abundance of ultradense minihalos, which can dominate the dark matter even at minuscule PBH fractions and are already constrained by microlensing. Together, these effects sharpen and transform the observational signatures of PBH dark matter.