Thermal Tachyacoustic Cosmology

Abstract

An intriguing possibility that can address pathologies in both early universe cosmology (i.e. the horizon problem) and quantum gravity (i.e. non-renormalizability), is that particles at very high energies and/or temperatures could propagate arbitrarily fast. A concrete realization of this possibility for the early universe is the Tachyacoustic (or Speedy Sound) cosmology, which could also produce a scale-invariant spectrum for scalar cosmological perturbations. Here, we study Thermal Tachyacoustic Cosmology (TTC), i.e. this scenario with thermal initial conditions. We find that a phase transition in the early universe, around the scale of Grand Unified Theories (GUT scale; $T\sim 10^{15}$ GeV), during which the speed of sound drops by $25$ orders of magnitude within a Hubble time, can fit current CMB observations. We further discuss how production of primordial black holes constrains the cosmological acoustic history, while coupling TTC to Horava-Lifshitz gravity leads to a lower limit on the amplitude of tensor modes ($r\gtrsim 10^{-3}$), that are detectable by CMBPol (and might have already been seen by the BICEP-Keck collaboration).

5 pages, 1 figure, comments are welcome

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Cited by in corpus (8)

• Probing microstructure of black hole spacetimes with gravitational wave echoes
• The critical geometry of a thermal big bang
• Spectrum of Cuscuton Bounce
• Theoretical implications of detecting gravitational waves
• The phenomenology of squeezing and its status in non-inflationary theories
• Primordial perturbations in a rainbow universe with running Newton constant
• The Trans-Planckian problem in Tachyacoustic Cosmology
• Non-Gaussian Signatures of a Thermal Big Bang