The Stringy Origins of Galileons and their Novel Limit

We show generalized Galileons – a particular subclass of Horndeski gravity – arise from a consistent Kaluza-Klein reduction of the low-energy effective action of heterotic string theory to first order in ${\alpha }^{\mathrm{\prime }}$. This suggests Horndeski theories of gravity have a string-theoretic origin. The form of the Galileonic terms is precisely fixed by parameters of the embedding spacetime, so that only a specific subset of Horndeski theories is permitted by string theory. A novel limit of the model is considered by performing a dimensionful rescaling of ${\alpha }^{\mathrm{\prime }}$.