DOMAIN-WALL SPACETIMES - INSTABILITY OF COSMOLOGICAL EVENT AND CAUCHYHORIZONS

The stability of cosmological event and Cauchy horizons of spacetimes associated with plane symmetric domain walls is studied. It is found t hat both horizons are not stable against perturbations of null fluids and massless scalar fields; they are turned into curvature singulariti es. These singularities are lightlike and strong in the sense that bot h the tidal forces and distortions acting on test particles become unb ounded when these singularities are approached.