Phase transitions and domain walls as a new route to primordial black holes

When the early universe undergoes a strong first-order phase transition, colliding bubbles and sound waves generate tensor perturbations; at second order, these source density fluctuations that can collapse into primordial black holes. The same mechanism works for annihilating domain walls. For phase transition temperatures between 400 GeV and 10 TeV and a narrow range of transition rates, asteroid-mass primordial black holes can comprise all dark matter, while the accompanying gravitational wave signal falls squarely in the LISA and SKA sensitivity bands. The framework yields model-independent constraints on both the cosmological phase transition parameters and the underlying particle physics — whether in the visible or dark sector — from existing primordial black hole abundance limits.