https://doi.org/10.1140/epjc/s10052-018-5575-9
Regular Article - Theoretical Physics
De Sitter stability and coarse graining
1
Department of Physics, Imperial College London, London, SW7 2AZ, UK
2
Department of Physics, King’s College London, Strand, London, WC2R 2LS, UK
* e-mail: t.markkanen@imperial.ac.uk
Received:
11
November
2017
Accepted:
18
January
2018
Published online:
2
February
2018
We present a 4-dimensional back reaction analysis of de Sitter space for a conformally coupled scalar field in the presence of vacuum energy initialized in the Bunch–Davies vacuum. In contrast to the usual semi-classical prescription, as the source term in the Friedmann equations we use expectation values where the unobservable information hidden by the cosmological event horizon has been neglected i.e. coarse grained over. It is shown that in this approach the energy-momentum is precisely thermal with constant temperature despite the dilution from the expansion of space due to a flux of energy radiated from the horizon. This leads to a self-consistent solution for the Hubble rate, which is gradually evolving and at late times deviates significantly from de Sitter. Our results hence imply de Sitter space to be unstable in this prescription. The solution also suggests dynamical vacuum energy: the continuous flux of energy is balanced by the generation of negative vacuum energy, which accumulatively decreases the overall contribution. Finally, we show that our results admit a thermodynamic interpretation which provides a simple alternate derivation of the mechanism. For very long times the solutions coincide with flat space.
© The Author(s), 2018
