If the speed of sound were vastly larger in the early Universe a nearscale-invariant spectrum of density fluctuations could have been produced evenif the Universe did not submit to conventional solutions to the horizonproblem. We examine how the mechanism works, presenting full mathematicalsolutions and their heuristics. We then discuss several concrete models basedon scalar fields and hydrodynamical matter which realize this mechanism, butstress that the proposed mechanism is more fundamental and general.
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