Fermi-ball dark matter from a first-order phase transition

Understand

We propose a novel dark matter (DM) scenario based on a first-order phase transition in the early universe.

• If dark fermions acquire a huge mass gap between true and false vacua, they can barely penetrate into the new phase.
• Instead, they get trapped in the old phase and accumulate to form macroscopic objects, dubbed Fermi-balls.
• We show that Fermi-balls can explain the DM abundance in a wide range of models and parameter space, depending most crucially on the dark-fermion asymmetry and the phase transition energy scale (possible up to the Planck scale).