THE VACUUM OF DE SITTER SPACE

To resolve infrared problems with the de Sitter invariant vacuum, de Sitter symmetry must be broken. We discuss how the history of the de Sitter phase is related to the infrared cutoff. We illustrate how either (1) the diagonalization of the Hamiltonian for long-wavelength modes or (2) an explicit modification of the metric in the distant past leads to natural infrared cutoffs. The former case resembles a bosonic superconductor in which graviton-pairing occurs between non-adiabatic modes. While the dynamical equations respect de Sitter symmetry, the vacuum is not de Sitter invariant because of the introduction of an initial condition at a finite time. In the latter case, we indicate just how infrared cutoffs are associated with modifications of the metric. The implications for the one-loop stress tenser and the production of particles are also discussed.