Speaker
Description
In this talk I am going to focus on the study of the power spectrum of the velocity field induced in the primordial plasma by expanding scalar-field bubbles during a first-order phase transition occurring in the radiation-dominated era.
Contrary to previous expectations, we find that the breaks in the velocity spectrum are not associated to the bubble size and the sound shell thickness,
but to the position of the discontinuities of the velocity profiles.
This distinction is particularly relevant for supersonic deflagrations,
as it implies that the intermediate slope is more pronounced and
the two breaks are more separated when the wall velocity approaches the Chapman-Jouget speed, instead of the sound speed.
Moreover, we find that the asymptotic branches of the velocity power
spectrum are determined by an integral over the velocity profiles at large scales, and by the discontinuities of the profiles at small scales. Furthermore, the position of the two breaks and the intermediate slope depend on the distribution function of the times of bubble nucleation.
The main result is a refined template for the velocity
spectrum at the beginning of the sound-wave phase,
which can be used for studying the resulting anisotropic stresses
and gravitational wave production.