Testing Affleck-Dine Baryogenesis with Gravitational Waves

The source of the observed cosmological baryon excess is unknown, but a popular proposal is Affleck-Dine baryogenesis. In this model, the asymmetry is produced during the evolution of a scalar condensate, which fragments into non-topological solitons (Q-balls). If these Q-balls are sufficiently long-lived, then they may dominate the energy density of the universe before decaying, releasing their baryon charge into the plasma. The decays of charged quanta into Standard Model fermions can occur only at the surface of the Q-ball, and so the decay rate increases as the Q-ball shrinks. From a cosmological perspective, Q-ball decay is effectively instantaneous, similar to black hole decay, and so the universe undergoes a rapid transition from matter to radiation domination. The Q-ball overdensities become sound waves in the plasma, which source gravitational waves, and a particular frequency is resonantly enhanced (as with primordial black holes, the so-called "poltergeist mechanism"). For well-motivated regions of parameter space, this peak is in the detectable range of the Einstein telescope and/or DECIGO, providing a new opportunity to test Affleck-Dine baryogenesis.