Gauss–Bonnet Inflation and the String Swampland

Abstract

The two swampland criteria are generically in tension with the single field slow-roll inflation because the first swampland criterion requires small tensor to scalar ratio while the second swampland criterion requires large tensor to scalar ratio. The challenge to the 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 swampland criteria may imply Gauss-Bonnet coupling.

Swampland implications of GW170817-compatible Einstein-Gauss-Bonnet gravity

“…Our result is somewhat more general in comparison to the one of Ref. [31], where the Swampland criteria were addressed in the context of Einstein-Gauss-Bonnet theories. As it was shown in [31], if the function ξ(φ) is chosen as ξ(φ) = λ V (φ) , and also certain assumptions are imposed on the scalar coupling function ξ(φ) and its derivatives with respect to the cosmic time, the theory satisfies the Swampland criteria.…”

“…Also in Ref. [31], the Swampland criteria were considered for Einstein-Gauss-Bonnet theories, like in our case, but from a different perspective, since the compatibility with the GW170817 event was not taken into account.…”

The Swampland: Introduction and Review

“…The conjectures were also considered as motivating cosmological scenarios qualitatively different from the usual ΛCDM or quintessence ideas . The interaction of theories of modified gravity with the de Sitter conjectures was studied in []. The conjectures were applied to properties of compact objects such as boson stars and primordial black holes .…”

Type I hilltop inflation and the refined swampland criteria

“…(19) are suppressed in M P , we can expect those terms to become important when φ → M P therefore M M P as in Eq. (15). We can also use dimensional analysis to the slow-roll parameter…”

“…There is a way out from the condition given by Eq. (15). The derivation of the condition is based on the conventioanl Friedmann equation ρ = 3H 2 M 2 P .…”