• Retaining only the dominant terms, the dilaton
perturbation satisfies
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• with the solution in k-space
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• Then, once the perturbations enter the causal
horizon dc (but are still outside the acoustic
horizon ds ), δΦ undergoes rapid damped oscillations, so that the nonadiabatic
perturbation associated
with Φ is destroyed. This
means that the nonadiabatic perturbations
are not automatically preserved except at long,
i.e., superhorizon, wavelengths where the simple Chaplygin gas has no problem anyway.
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