In theoretical physics, F-theory is a branch of string theory developed by Iranian-American physicist Cumrun Vafa.
[1] The new vacua described by F-theory were discovered by Vafa and allowed string theorists to construct new realistic vacua — in the form of F-theory compactified on elliptically fibered Calabi–Yau four-folds.
The SL(2,Z) S-duality symmetry of the resulting type IIB string theory is manifest because it arises as the group of large diffeomorphisms of the two-dimensional torus.
[4] New models of Grand Unified Theory have recently been developed using F-theory.
[5] F-theory has the metric signature (10,2), which means that it includes a second time dimension.