Abstract
We study the constraint on the inflationary energy scale from the recently proposed trans-Planckian censorship conjecture (TCC). We find a universal upper bound on the inflationary Hubble expansion rate which is solely determined by the reheating temperature : , where is the photon temperature today. The upper limit can be saturated by a postinflationary oscillatory stage with the critical equation-of-state parameter , or by an inflation model with multiple stages. In the lowest reheating temperature required for big bang nucleosynthesis, the upper bound on the tensor-to-scalar ratio at the CMB scales is , which can be realized in many string-inspired inflation models.
- Received 9 November 2019
- Accepted 22 June 2020
DOI:https://doi.org/10.1103/PhysRevD.102.021301
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