Patient observers and IR issues in cosmology

by Martin Sloth (SDU, Odense)

Thursday 7 Jun 2018, 14:00 → 15:00 Europe/Berlin

3344 (Physikdepartment)

It is well known that massless scalar fields as well as well as graviton fluctuations exhibit infrared divergences in de Sitter and inflationary space-times. Analogous to how the related problem was resolved for QED in the 60ties, I will discuss how the issue can be resolved in cosmology by properly defining local observables, and how consistency relations for the infrared part of loops can be derived. I will then discuss the relation between local observers seeing small effects and global observables exhibiting large infrared effects, and link it to the on-going discussion regarding whether the Maldacena consistency relation is physical. In the a second part of the talk, I will discuss the relation to asymptotic symmetries of the de Sitter spacetime, construct the associated charges, and show that acting with the charges is equivalent to a change in the local coordinates induced by a soft graviton. Finally, I will discuss the lack of local observability of IR effects even to "patient observers", and make comparisons with a related discussion of black hole evaporation.