Finite particle creation in 3+1 de Sitter space
  In this paper we calculate the particle creation as seen by a stationary observer in 3+1 de Sitter space. This particle creation is calculated using an observer dependent geometrically based definition of time which is used to quantize a field on two different spacelike surfaces. The Bogolubov transformation relating these two quantizations is then calculated and the resulting particle creation is shown to be finite. 
D.J. Lamb, A.Z. Capri and M. Kobayashi