Superexpansionary divergence: breakdown of perturbative quantum field theory in spacetime with accelerated expansion

The authors show that perturbative quantum field theory may break down in curved spacetime with accelerated expansion. They consider lambda phi p -theory (p=3,4,5,. . .) with curvature coupling xi R phi 2 in de Sitter space and perturbatively evaluate the n-point function. They find the vertex integral over all spacetime points diverges for a certain range of the mass and curvature coupling. In particular, for lambda phi 4 theory with xi =0, the divergence arises for m 2 /H 2 <or= 27 / 16 where H -1 is the de Sitter radius. Then, they show that the same type of divergence arises quite generally in a spacetime with accelerated expansion. Since it is caused by unboundedly accelerated expansion of spacetime, they call it the superexpansionary divergence.