Gauge fluxes in F-theory and type IIB orientifolds

We provide a detailed correspondence between G4 gauge fluxes in F-theory compactifications with SU(n) and SU(n) × U(1) gauge symmetry and their Type IIB orientifold limit. Based on the resolution of the relevant F-theory Tate models, we classify the factorisable G4-fluxes and match them with the set of universal D5-tadpole free U(1)-fluxes in Type IIB. Where available, the global version of the universal spectral cover flux corresponds to Type IIB gauge flux associated with a massive diagonal U(1). In U(1)-restricted Tate models extra massless abelian fluxes exist which are associated with specific linear combinations of Type IIB fluxes. Key to a quantitative match between F-theory and Type IIB is a proper treatment of the conifold singularity encountered in the Sen limit of generic F-theory models. We also shed further light on the brane recombination process relating generic and U(1)-restricted Tate models.