We study Tachyacoustic models of cosmology, for which a scale-invariant perturbation spectrum is generated via superluminal sound speed instead of accelerated expansion, as in the case of inflation. We derive two bounds on the size of acoustic horizon which constrain the duration of tachyacoustic evolution, and therefore generation of primordial perturbations. We show that existing models cannot solve the horizon problem without violating the condition that all physical scales — such as the Hubble parameter, the pressure, and the length scale at which quantum modes freeze out and become classical — be sub-Planckian.

中文翻译：

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快速声学宇宙学中的跨普朗克问题

我们研究宇宙学的快速声学模型，通过超光速声速而不是加速膨胀来生成尺度不变的扰动谱，就像在暴胀的情况下一样。我们推导出声学视界大小的两个界限，这两个界限限制了快速声学演化的持续时间，从而限制了原始扰动的产生。我们表明，现有模型无法在不违反所有物理尺度（例如哈勃参数、压力和量子模式冻结并成为经典的长度尺度）都是亚普朗克的条件的情况下解决视界问题。