Gravitational waves and gamma-ray observatories as multi-messenger probes of first-order phase transitions and intergalactic magnetic fields

by Alberto Roper Pol (Geneva University)

Thursday 18 Jan 2024, 15:00 → 16:30 Europe/Berlin

seminar room 3 (bldg. 1b)

Gravitational waves (GW) can be produced by several mechanisms in the early Universe, yielding a cosmological gravitational wave background that we might detect in the coming years with space-based detectors like LISA and next-generation ground-based detectors like ET or CE, or might have already been detected by pulsar timing array (PTA) collaborations. I will review the recent PTA observations and their possible connection to cosmological sources of GWs. In the early Universe, the primordial plasma is highly coupled to magnetic fields if present, leading to the development of magnetohydrodynamic (MHD) turbulence. I will show some analytical estimates and recent results of numerical simulations that address the production of GWs in a first-order phase transition from sound waves and MHD turbulence. In general, magnetic fields produced in the early Universe would then evolve until present time and could serve as an explanation for the indirect observation of intergalactic magnetic fields at the largest scales of our Universe by the Fermi collaboration. These observations allow us to explore primordial magnetic fields in a multi-messenger approach: by their effect on the cosmological gravitational wave background, their impact on the CMB, and their astrophysical consequences.