Paulina Schlachter (Vienna): Particle Production at a Cosmological First-Order Phase Transition

In the first few fractions of a second after the Big Bang, the universe rapidly went through a series of different phases as it cooled down, each phase correspondingto the breaking of a certain symmetry. Under certain conditions, this symmetry breaking happens through a cosmological first-order phase transition which would happen through the nucleation and expansion of bubbles of the ”broken” phase. Such a supercooled phase transition would dilute away all pre-existing dark matter in the universe, necessitating a mechanism to create dark matter during or after the phase transition. The mechanism proposed is as follows:
Since translational symmetry is broken across the boundary between the two phases, conservation of momentum is no longer given and exotic processes that would normally be forbidden become possible. One such process would be the decay of a light scalar, which is taken to be the order parameter of the phase transition, into two heavy fermionic particles which gain a significant amount of mass through a Yukawa-type interaction. So far, the decay into fermionic dark matter has only been studied through non-renormalizable interactions. We find that there is a marginal operator describing this process and present some preliminary numerical calculations pertaining to the number density of produced particles.