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 $\alpha'$. 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 $\alpha'$.