Lyth bound revisited

Qing-Guo Huang
Phys. Rev. D 91, 123532 – Published 22 June 2015

Abstract

Imposing that the excursion distance of the inflaton in field space during inflation be less than the Planck scale, we derive an upper bound on the tensor-to-scalar ratio at the cosmic microwave background scales, i.e., r*,max, in the general canonical single-field slow-roll inflation model, in particular, the model with non-negligible running of the spectral index αs and/or the running of running βs. We find that r*,max7×104 for ns=0.9645 without running and running of running, and r*,max is significantly relaxed to the order of O(102101) in the inflation model with αs and/or βs+O(102) which are marginally preferred by the Planck 2015 data.

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  • Received 19 March 2015

DOI:https://doi.org/10.1103/PhysRevD.91.123532

© 2015 American Physical Society

Authors & Affiliations

Qing-Guo Huang*

  • State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Science, Beijing 100190, People’s Republic of China

  • *huangqg@itp.ac.cn

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Issue

Vol. 91, Iss. 12 — 15 June 2015

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