Propagators in de Sitter space

Understand

In a spacetime with no global timelike Killing vector, we do not have a natural choice for the vacuum state of matter fields, leading to an ambiguity in defining the Feynman propagators.

• In this paper, taking the vacuum state to be the instantaneous ground state of the Hamiltonian at each moment, we develop a method for calculating wave functions associated with the vacuum and the corresponding in-in and in-out propagators.
• We apply this method to free scalar field theory in de Sitter space and obtain de Sitter invariant propagators in various coordinate patches.
• We show that the in-out propagator in the Poincare patch has a finite massless limit in a de Sitter invariant form.