Speaker
Description
Black holes in the asteroid-mass range, $10^{15}$ - $10^{20}$ kg, provide a compelling candidate for dark matter. This window remains largely unconstrained observationally, while the low masses provide an interesting challenge in explaining their possible origin. In this talk, I will discuss a particular formation scenario of such objects, where curvature perturbations responsible for gravitational collapse into black holes are generated by a cosmological first-order phase transition. If the transition is strongly supercooled and slow compared to the Hubble expansion, fluctuations in the bubble nucleation history in different patches of the Universe can produce a large spectrum of curvature perturbations. I will present a covariant formalism that can be adopted to compute the evolution of energy-density fluctuations within a fixed comoving volume. Within this formalism, I will highlight the crucial role of energy flux carried by expanding bubble walls in amplifying curvature perturbations to the level required for black hole formation. Finally, I will identify the transitions for which the population of produced black holes can fully explain the abundance of dark matter observed today.