Speedy sound and cosmic structure

Understand

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.