Speaker
Description
While cooling down, the early universe is believed to have undergone symmetry breaking phase transitions. One attractive possibility for extending the Standard Model is that these phase transitions are of the first order, as they might be able to produce observable gravitational waves. We consider a dark matter freeze-out mechanism, filtering, where dark matter particles become massive in a first order phase transition. Since the mass of the dark matter increases at the phase boundary, only sufficiently energetic particles are able to enter the bubbles of the new phase, while others are reflected and will be annihilated. We focus specifically on a subset of phase transitions, deflagrations, during which the bubble walls are subsonic and slowed down as they expand. As the transition proceeds, this causes heated droplets of metastable vacuum to be formed. In the droplet stage the wall velocity and the temperature profile differ from the initial asymptotic expansion profile. We examine these parameters and evaluate how they affect the dark matter production. We have found that different amounts of dark matter are produced during the initial expansion and the final slowed down droplet stage. Taking this into account, we calculate a realistic estimate for the dark matter relic abundance produced by filtering in deflagration scenarios.