Horndeski in the Swampland

Abstract

We investigate the implications of string Swampland criteria for alternative theories of gravity. Even though this has not rigorously been proven, there is some evidence that exact de-Sitter solutions with a positive cosmological constant cannot be successfully embedded into string theory, and that the low energy effective field theories containing a scalar field $\pi$ with a potential $V$ in the habitable landscape should satisfy the Swampland criteria $|V^{\prime }|/V\ge c\sim \mathcal{O}(1)$. As a paradigmatic class of modified gravity theories for inflation and dark energy, we consider the extensively studied family of Horndeski Lagrangians in view of cosmological observations. Apart from a possible potential term, they contain derivative self-interactions as the Galileon and non-minimal couplings to the gravity sector. Hence, our conclusions on the Galileon sector can be also applied to many other alternative theories with scalar helicity modes containing derivative interactions such as massive gravity and generalized Proca. In the presence of such derivative terms, the dynamics of the scalar mode is substantially modified, and imposing the cosmological evolution constrained by observations places tight constraints on $c$ within the Swampland conjecture.

8 pages, 5 figues, published version

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• Swampland Criteria in the Slotheon Field Dark Energy
• Constraints on dark energy models from the Horndeski theory
• Stability, dark energy parameterization and swampland aspect of Bianchi Type-$V{I}_h$ cosmological models with f(R, T)-gravity
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• Scalar-Connection Gravity and Spontaneous Scalarization
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• Refined Swampland conjecture in deformed Starobinsky gravity
• The Stringy Origins of Galileons and their Novel Limit
• Exponential quintessence with momentum coupling to dark matter
• How Much NEC Breaking Can the Universe Endure?
• Hitchhiker's Guide to the Swampland: The Cosmologist's Handbook to the string-theoretical Swampland Programme
• Lanczos equation on light-like hypersurfaces in a cosmologically viable class of kinetic gravity braiding theories
• Cosmic acceleration from string induced Galileons