SUPEREXPANSIONARY DIVERGENCE - BREAKDOWN OF PERTURBATIVE QUANTUM-FIELD THEORY IN SPACETIME WITH ACCELERATED EXPANSION

We show that perturbative quantum field theory may break down in curved spacetime with accelerated expansion. We consider lambdaphi(p)-theory (p = 3, 4,5,...) with curvature coupling xiRphi2 in de Sitter space and perturbatively evaluate the n-point function. We find the vertex integral over all spacetime points diverges for a certain range of the mass and curvature coupling. In particular, for lambdaphi4 theory with xi = 0, the divergence arises for M2/H-2 less-than-or-equal-to 27/16 where H-1 is the de Sitter radius. Then we 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, we call it the superexpansionary divergence.