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Gauss–Bonnet Inflation and the String Swampland

1
Department of Astronomy, Beijing Normal University, Beijing 100087, China
2
School of Physics, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China
*
Author to whom correspondence should be addressed.
Universe 2019, 5(9), 200; https://doi.org/10.3390/universe5090200
Received: 22 August 2019 / Revised: 10 September 2019 / Accepted: 12 September 2019 / Published: 15 September 2019
(This article belongs to the Special Issue Inflation, Black Holes and Gravitational Waves)
The swampland criteria are generically in tension with single-field slow-roll inflation because the first swampland criterion requires small tensor-to-scalar ratio while the second swampland criterion requires either large tensor-to-scalar ratio or large scalar spectral tilt. The challenge to single-field slow-roll inflation imposed by the swampland criteria can be avoided by modifying the relationship between the tensor-to-scalar ratio and the slow-roll parameter. We show that the Gauss–Bonnet inflation with the coupling function inversely proportional to the potential overcomes the challenge by adding a constant factor in the relationship between the tensor-to-scalar ratio and the slow-roll parameter. For the Gauss–Bonnet inflation, while the swampland criteria are satisfied, the slow-roll conditions are also fulfilled, so the scalar spectral tilt and the tensor-to-scalar ratio are consistent with the observations. We use the potentials for chaotic inflation and the E-model as examples to show that the models pass all the constraints. The Gauss–Bonnet coupling seems a way out of the swampland issue for single-field inflationary models. View Full-Text
Keywords: inflation; Gauss–Bonnet inflation; swampland inflation; Gauss–Bonnet inflation; swampland
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Yi, Z.; Gong, Y. Gauss–Bonnet Inflation and the String Swampland. Universe 2019, 5, 200.

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