Gauge threshold corrections for local type-IIB/F-theory GUTs

We study gauge threshold corrections for local grand unified theory models in IIB/F-theory. Consistency with holomorphy requirements of supergravity and the Kaplunovsky-Louis formula implies that the unification scale is enhanced by the bulk radius R from the string scale to M-X=RMS. We argue that the stringy interpretation of this is via a locally uncanceled tadpole sourced by the hypercharge flux. This sources closed string modes propagating into the bulk-equivalently open string gauge coupling running up to the winding scale M-X. The enhancement to RMs is tied to grand unified theory breaking by a globally trivial hypercharge flux and will occur in all models realizing this mechanism.