One Loop Graviton Self-Energy In A Locally De Sitter Background

The graviton tadpole has recently been computed at two loops in a locally de Sitter background. We apply intermediate results of this work to exhibit the graviton self-energy at one loop. This quantity is interesting both to check the accuracy of the first calculation and to understand the relaxation effect it reveals. In the former context we show that the self-energy obeys the appropriate Ward identity. We also show that its flat space limit agrees with the flat space result obtained by Capper in what should be the same gauge.Comment: 35 pages, plain TeX, 4 Postscript files, uses psfig.sty, revised June 1996 for publication in Physical Review

Matter Contributions to the Expansion Rate of the Universe

We consider the effect of various particles on the cosmic expansion rate relative to that of the graviton. Effectively massless fermions, gauge bosons and conformally coupled scalars make only minuscule contributions due to local conformal invariance. Minimally coupled scalars can give much stronger contributions, but they are still sub-dominant to those of gravitons on account of global conformal invariance. Unless effectively massless scalar particles with very particular couplings exist, the leading effect on the expansion rate is furnished solely by the graviton. An upper bound on the mass of such scalar particles is obtained.Comment: 14 pages, plain TeX, 7 Postscript files, uses psfig.st

Quantum Gravity Slows Inflation

We consider the quantum gravitational back-reaction on an initially inflating, homogeneous and isotropic universe whose topology is $T^3 \times \Re$. Although there is no secular effect at one loop, an explicit calculation shows that two-loop processes act to slow the rate of expansion by an amount which becomes non-perturbatively large at late times. By exploiting Feynman's tree theorem we show that all higher loops act in the same sense.Comment: 19 pages, plain TeX, 1 Postscript file, uses psfig.sty, revised June 1996 for publication in Nuclear Physics