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Gauss–Bonnet Inflation and the String Swampland

Department of Astronomy, Beijing Normal University, Beijing 100087, China
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;
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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