The Trans-Planckian problem in Tachyacoustic Cosmology

Abstract

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.

6 pages, 1 figure (v2: new section added.)

References in corpus (9)

• Trans-Planckian Censorship and the Swampland
• Trans-Planckian Censorship and Inflationary Cosmology
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• Speedy sound and cosmic structure
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Cited by in corpus (2)

• Hitchhiker's Guide to the Swampland: The Cosmologist's Handbook to the string-theoretical Swampland Programme
• Trans-Planckian Censorship Conjecture and Early Universe Cosmology