  Causal seed models, such as cosmological defects, generically predict a
distinctly different structure to the CMB power spectrum than inflation, due to
the behavior of the perturbations outside the horizon. We provide a general
analysis of their causal generation from isocurvature initial conditions by
analyzing the role of stress perturbations and conservation laws in the causal
evolution. Causal stress perturbations tend to generate an isocurvature pattern
of peak heights in the CMB spectrum and shift the first compression, i.e.~main
peak, to smaller angular scales than in the inflationary case, unless the
pressure and anisotropic stress fluctuations balance in such a way as to
reverse the sense of gravitational interactions while also maintaining constant
gravitational potentials. Aside from this case, these causal seed models can be
cleanly distinguished from inflation by CMB experiments currently underway.

Astrophysics;General Relativity and Quantum Cosmology;High Energy Physics - Phenomenology