  If the speed of sound were vastly larger in the early Universe a near
scale-invariant spectrum of density fluctuations could have been produced even
if the Universe did not submit to conventional solutions to the horizon
problem. We examine how the mechanism works, presenting full mathematical
solutions and their heuristics. We then discuss several concrete models based
on scalar fields and hydrodynamical matter which realize this mechanism, but
stress that the proposed mechanism is more fundamental and general.

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