Abstract: Gravitational waves (GWs) can be produced by a first-order phase transition in the early Universe via the fluid perturbations induced in the primordial plasma by the expansion and collision of broken-phase bubbles. I will review the production of GWs by the anisotropic stresses of velocity and magnetic fields induced in a first-order phase transition and present recent developments on the analytical estimates and numerical simulations that address the stochastic GW background produced by acoustic motion (sound waves) and magnetohydrodynamic (MHD) turbulence. These GWs could be detectable by current and future GW detectors like LISA or PTA, potentially providing us with direct clean information of the physics at the high energies of the early Universe and probing beyond the Standard Model physics. In addition, the presence of magnetic fields at a phase transition leads to coupled non-linear fluid perturbations, described by MHD turbulence, that will impact the cosmological GW background. The study of these effects can be used to put constraints on primordial magnetic fields. These fields would evolve until present time and leave observable imprints in, for example, the CMB and in the cosmic voids of the large-scale structure of the Universe, allowing us to combine GW observations with other cosmological and astrophysical observations in a multi-messenger approach.

This seminar is part of the "Holography in the Gravitational Wave Era” (HOLOGW) project (with grant agreement number 101141909) funded by the European Union / ERC: