Speaker
Description
Minuscule primordial black holes produced just after inflation can serve as time capsules" bringing back energy from the past to a later epoch when they evaporate. As these black holes behave like matter, while the rest of the Universe content behaves like radiation, the mass fraction of these black holes, that is tiny at formation, becomes significant later. If sufficiently small, these black holes will evaporate while the Universe is still radiation dominated. I discuss this process and in particular the prospect that BH evaporation can producedark radiation" in the form of gravitons that is homogeneous and free of Silk damping. With suitable but extreme parameters, this background graviton field can resolve the Hubble tension. I contrast this idea with another mechanism for the formation of gravitons background field, annihilation of particles at the Planck era and discuss possible ways to distinguish between the two backgrounds.