  First order phase transitions in the early universe naturally lead to the
production of a stochastic background of gravitational waves and to the
generation of a matter-antimatter asymmetry. The dynamics of the phase
transition is affected by the density perturbations in the hot plasma. We
address this topic by providing, for the first time, a full numerical solution
to the linearized Boltzmann equation for the top quark species coupled to the
Higgs field during a first order phase transition at the electroweak scale.
Differently from the traditional approaches, our results do not depend on any
ansatz and can fully describe the non-equilibrium distribution functions of the
particle species in the plasma.
