Abstract
Motivated by black hole physics, we define the Unruh state for a scalar field in de Sitter space. Like the Bunch-Davies state, the Unruh-de Sitter state appears thermal to a static observer. However, it breaks some of the symmetries of de Sitter space. We calculate the expectation value of the energy-momentum tensor in the Unruh-de Sitter state in two dimensions and find a non-vanishing flux of outgoing negative energy. Extrapolating the result to four dimensions, we argue that this backreacts on the initial de Sitter geometry semi-classically. Notably, we estimate that de Sitter space is destabilized on a timescale set by the gravitational entropy; analogous to black hole evaporation, the endpoint of this instability is a singular geometry outside the regime of effective field theory. Finally, we suggest that the Unruh-de Sitter state may be a natural initial state for patches of de Sitter space, and discuss the implications for slow-roll and eternal inflation, and for de Sitter thermodynamics.
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ArXiv ePrint: 1905.02714
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Aalsma, L., Parikh, M. & van der Schaar, J.P. Back(reaction) to the future in the Unruh-de Sitter state. J. High Energ. Phys. 2019, 136 (2019). https://doi.org/10.1007/JHEP11(2019)136
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DOI: https://doi.org/10.1007/JHEP11(2019)136