A note on modular invariant species scale and potentials

Abstract

The species scale provides an upper bound for the ultraviolet cutoff of effective theories of gravity coupled to a number of light particle species. We point out that modular invariant (super-)potentials provide a simple and computable expression of the species scale as a function of the moduli in toroidal orbifold compactifications of type II and heterotic string. Due to modular symmetry, these functions are valid over all moduli space and not only in asymptotic regions. We observe that additive logarithmic corrections to the species scale arise from the requirement that the latter be modular invariant. We recast the moduli-dependent expression of the species scale in terms of the gravitino mass or the scalar potential of these models and we connect it to swampland conjectures such as the anti-de Sitter distance conjecture and the gravitino conjecture.