Domain boundaries, Goldstone bosons and gravitational waves

The dynamical behaviour of domain boundaries between different realizations of the vacuum of scalar fields with spontaneously broken phases is investigated. They correspond to zero-modes of the Goldstone fields, moving with the speed of light, and turn out to be accompanied by strongly oscillating gravitational fields. In certain space-time topologies this leads to a quantization condition for the symmetry breaking scale in terms of the Planck mass.