DOMAIN-WALLS IN A FRW UNIVERSE

We solve the equations of motion for a scalar field with domain wall b oundary conditions in a Friedmann-Robertson-Walker (FRW) spacetime. We find (in agreement with Basu and Vilenkin) that no domain wall soluti ons exist in de Sitter spacetime for h equivalent to H/m greater than or equal to 1/2, where H is the Hubble parameter and m is the scalar m ass. in the general FRW case we develop a systematic perturbative expa nsion in h to arrive at an approximate solution to the held equations. We calculate the energy-momentum tensor of the domain wall configurat ion, and show that the energy density can become negative at the core of the defect for some values of the nonminimal coupling parameter xi. We develop a translationally invariant theory for fluctuations of the wall, obtain the effective Lagrangian for these fluctuations, and qua ntize them using the Bunch-Davies vacuum in the de Sitter case. Unlike previous analyses, we find that the fluctuations act as zero-mass (as opposed to tachyonic) modes. This allows us to calculate the distorti on and the normal-normal correlators for the surface. The normal-norma l correlator decreases logarithmically with the distance between point s for large times and distances, indicating that the interface becomes rougher than in Minkowski spacetime.