Tufts/CfA/MIT Cosmology Seminar, at MIT:

                     Tuesday October 15, 1996
                             2:30 pm
                         CTP Seminar Room

              "Gauge Invariance and Back Reaction of 
                    Cosmological Perturbations"

                            Raul Abramo
                          Brown University

Abstract: 
In order to study the back reaction of gravitational perturbations in
General Relativity it is necessary to define a gauge-invariant effective
energy-momentum tensor for the perturbations.
To prove gauge invariance we need to keep track of the
effect of diffeomorphism transformations up to second order.
We derive the effective energy-momentum tensor of cosmological
perturbations about a FRW background and apply the results to
study back reaction in inflationary Universe models.
We found that the back reaction of cosmological perturbations on the 
background can become important already at
energies below the self-reproduction scale.