Entanglement in an expanding universe

by Prof. Nikolaos Tetradis (University of Athens)

Wednesday 24 Apr 2024, 16:15 → 18:15 Europe/Berlin

Abbeanum/Ground floor-HS 2 - Hörsaal 2 (TPI, FSU Jena)

I shall discuss the evolution of entanglement entropy for a massless field within a spherical region throughout the inflationary period and the subsequent era of radiation domination, starting from the Bunch-Davies vacuum. Each field mode evolves towards a squeezed state upon horizon exit during inflation, with additional squeezing when radiation domination sets in. This results in the enhancement entanglement entropy. Shortly after the transition to the radiation-dominated era, a volume term develops and becomes the leading contribution to the entropy at late times, as is common for systems lying in squeezed states.
I shall discuss the interpretation of the entropy in the light of the quantum to classical transition for modes exiting the horizon during inflation. Entanglement could be a means to track the quantum origin of weakly interacting fields, such as gravitational waves resulting from tensor modes during inflation, in today's universe. On the other hand, an observer with no knowledge of the degrees of freedom beyond the horizon would interpret the entropy as thermal. From this point of view, the reheating after inflation would be a result of quantum entanglement. I shall also present preliminary results on the precise expression for the entropy in de Sitter space, and I shall speculate on the possibility to check these results in analogue gravity experiments.