Antonino Salvino Midiri (Geneva U.): Acoustic fluid perturbations in first-order phase transitions
Albano 3: 4205 - SU Conference Room (40 seats)
Albano Building 3
Title: Acoustic fluid perturbations in first-order phase transitions
Abstract: First-Order Phase Transitions in the early Universe can source a Stochastic Gravitational Wave Background. If they occur at the electroweak scale, the resulting Gravitational Wave spectrum can peak in the LISA sensitivity band. Many processes in a First-Order Phase Transition can contribute to the resulting Gravitational Wave spectrum. The expanding scalar broken-phase bubbles can produce longitudinal perturbations in the primordial plasma which lead, after bubble collisions, to the development of sound waves. Moreover, due to the production of shocks, both across and after collisions, vorticity can be generated in the fluid, which, in the presence of magnetic fields, due to the high conductivity of the plasma, can lead to magnetohydrodynamic turbulence. A full understanding of the interplay between these processes is a challenging problem which requires both lattice simulations and analytical efforts. In this talk I will focus on the contribution from sound waves showing, in particular, the fundamental steps required to understand the properties of the Gravitational Wave spectrum starting from the fluid perturbations generated in the bubble expansion phase. The main result is an analytical prediction for the dependence on the phase transition parameters of the peak frequency scales in the Gravitational Wave spectrum.