2.2.4. DOMAIN WALLS
The GUTs phase transition produces certain characteristic
discontinuities in the matter distribution. This happens during the
spontaneous breakdown of symmetry, which leads the mediating scalar
fields to have a discrete set of characteristic values. Thus one
region or ``domain'' has one value of the scalar field, while its
neighbor has another.
The boundary wall between the domains would therefore be a region of
discontinuity. We expect to see this as a sheet of inhomogeneity in
the large scale matter distribution in the universe. The present data
do not reveal any such inhomogeneity in the observable universe.