Type IIA on Spin (7) manifolds with fluxes

A bstract We initiate a systematic study of compactifications of type II string theory to two dimensions on Ricci-flat spaces with fluxes and sources. We derive universal constraints on such compactifications, and then develop type IIA compactifications on Spin(7)-holonomy spaces with bulk fluxes whose tadpole is cancelled by OF1-planes. We derive the resulting two-dimensional 𝒩 = (1, 1) supergravity for a toroidal Spin(7) orbifold, and we extend the metric and universal sectors geometrically to general compact Spin(7) manifolds. In candidate supersymmetric Minkowski vacua, all untwisted shape modes appear in the flux scalar potential and can in principle be classically stabilised. However, in an explicit toroidal orbifold example flux quantisation together with the tadpole bound may obstruct the existence of candidate vacua supported entirely within the untwisted sector. Within the approximation retaining the topological curvature contribution and its associated energy while neglecting the remaining higher-derivative corrections, the string-frame volume in string units is bounded by 7 χ /192, so suppressing α ′ corrections requires Spin(7) manifolds with large Euler characteristic.