  Using a large N sigma model approximation we explicitly calculate the power
spectrum of gravitational waves arising from a global phase transition in the
early universe and we confirm that it is scale invariant, implying an
observation of such a spectrum may not be a unique feature of inflation.
Moreover, the predicted amplitude can be over 3 orders of magnitude larger than
the naive dimensional estimate, implying that even a transition that occurs
after inflation may dominate in Cosmic Microwave Background polarization or
other gravity wave signals.
