Taxonomy of type II orientifold flux vacua in 3D

A bstract We complete the study initiated in [ JHEP 12 (2024) 087] and investigate three-dimensional (3D) flux vacua of type II orientifold reductions on twisted tori that include a single type of spacetime-filling O p -plane with p = 2, . . . , 9. Restricting to SO(3)-invariant setups — also known as RSTU-models — and setting axions to zero, we exhaustively chart the landscape of 3D orientifold flux vacua. It consists of 56 inequivalent multi-parametric families of AdS 3 and Mkw 3 flux vacua, all of them without negative masses in the spectrum of scalar fluctuations. Performing T-dualities, all the inequivalent vacua can be found in type IIB with either O9-, O5- or O3-planes. We show that: i ) type IIB with O9 fails to stabilise the volume of the internal space. ii ) type IIB with O5 realises the only cases of scale-separated AdS 3 vacua. iii ) type IIB with O3 provides only Mkw 3 vacua exhibiting a rich variety of supersymmetry-breaking patterns. Assuming that some mechanism (possibly non-perturbative) fixes the unstabilised modulus in type IIB with O9, we re-examine the possibility of achieving a weakly-coupled and scale-separated regime.