The scale at which quantum gravitational effects become manifest, the species scale, has been argued to take values parametrically lower than the Planck scale. It is therefore of interest to quantum gravity phenomenology to have a precise definition of how to compute this scale in any EFT that has a UV completion in quantum gravity. Two proposals have been made in the litterature, of different conceptual origin; one linked to the size of the smallest black hole that one can describe in an EFT and the other to the scale of higher-derivative corrections to the EFT. Arguably one of the most profound aspects of a theory of quantum gravity is that it should be background independent and that dynamics should only "emerge" as a low-energy description. I will demonstrate how a notion of "emergence" unifies the two definitions of the species scale.
I will do so by studying small (singular) black hole solutions in string theory and illustrating how higher-derivative corrections obtained from "emergence" correct these solutions and generate a species scale sized horizon for them.
Based on arXiv:2310.04488.