Existence of parametrically scale-separated string compactifications

Establish whether there exist string compactifications whose low-energy effective theories exhibit a cosmological constant that is parametrically separated from the Kaluza–Klein scale, thereby realizing genuine scale separation in string theory.

Background

The paper investigates the longstanding issue of scale separation in string compactifications, namely whether the cosmological constant can be made parametrically smaller than the Kaluza–Klein scale in a controlled setting. This topic is closely tied to swampland considerations and holography, where the general viability of such vacua is debated.

The work contributes by constructing scale-separated AdS3 vacua in massless type IIA with only O6-planes (obtained via double T-duality from massive IIA G2 compactifications), but emphasizes that the overarching question of the existence of parametrically scale-separated vacua in string theory remains unresolved in full generality.