Horndeski in the Swampland

Understand

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 $|V'|/V\ge c\sim\mathcal{O}(1)$.
• 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.