Quantum Stress Tensor Fluctuations of a Conformal Field and Inflationary
  Cosmology
  We discuss the additional perturbation introduced during inflation by quantum
stress tensor fluctuations of a conformally invariant field such as the photon.
We consider both a kinematical model, which deals only with the expansion
fluctuations of geodesics, and a dynamical model which treats the coupling of
the stress tensor fluctuations to a scalar inflaton. In neither model do we
find any growth at late times, in accordance with a theorem due to Weinberg.
What we find instead is a correction which becomes larger the earlier one
starts inflation. This correction is non-Gaussian and highly scale dependent,
so the absence of such effects from the observed power spectra may imply a
constraint on the total duration of inflation. We discuss different views about
the validity of perturbation theory at very early times during which currently
observable modes are transplanckian.
