This paper reports the first constructions of two-dimensional anti-de Sitter (AdS2) “flux vacua” in which the length scales of the hidden internal space can be made parametrically different from the AdS2 curvature scale. In plain terms, the authors show examples where the extra dimensions in a string-theory model can be made consistently much larger (or smaller) than the external spacetime curvature by dialing certain integer flux numbers. Such a separation of scales is useful for model building and for testing ideas about holography, where a lower-dimensional AdS space may admit a simpler dual description.

To get these examples the authors compactified type II string theory on an eight-dimensional internal geometry built from a seven-dimensional G2-structure orbifold times a circle. They include spacetime-filling orientifold planes (O1/O5 in type IIB, or O4/O8 in type IIA) that are treated as “smeared,” and they turn on two kinds of background fluxes (called NSNS and RR fluxes) that thread the internal cycles. From this setup they derive a two-dimensional dilaton-gravity effective theory and identify families of solutions. Concretely, in type IIB the unbounded five-form flux F5 and a seven-form flux H7 provide the tuning knob, while in type IIA the tunable fluxes are F4, F8 and H7.

Why this matters: by increasing the integer flux quanta the authors show that the string coupling becomes parametrically weak, all internal bulk radii become parametrically large in string units, and the Kaluza–Klein (KK) scale — the energy scale of excitations associated with the compact dimensions — separates from the AdS2 curvature scale. In other words, low-energy physics in the two-dimensional spacetime can decouple from the physics of the internal space. The paper also studies supersymmetry by analyzing the ten-dimensional Killing-spinor equations and identifies branches that preserve N=(1,1) supersymmetry in two dimensions. They further explain how these geometrically scale-separated solutions avoid conflicts with a recent no-go theorem that constrains scale separation in theories with extended supersymmetry. The authors also map out related solutions obtained by standard T-duality operations.