The CMB as a detector of gravitational waves

by Camilo Garcia Cely (DESY)

Tuesday 5 Oct 2021, 12:00 → 13:00 Europe/Madrid

IFAE Virtual Seminar Room (IFAE)

In complete analogy with axion dark matter, gravitational waves are converted into electromagnetic radiation when they propagate in magnetic fields. I will explain how this effect can be used to detect gravitational waves. With this in mind, I will examine gamma-ray observations by Fermi-LAT and HESS strongly suggesting the existence of a non-vanishing cosmic magnetic field. Then, I will show how the consequent conversion of gravitational waves into radio waves might distort the CMB, leading to bounds that exceed those from current terrestrial experiments. I will discuss prospects from the future gamma-ray observatory CTA and argue that future advances in 21 cm astronomy might push these bounds below the Neff constraint on the radiation density present during the CMB formation. Based on: PhysRevLett.126.021104