Vafa, Cumrun2019-09-221996Vafa, Cumrun. 1996. “Evidence for F-Theory.” Nuclear Physics B 469 (3): 403–15. https://doi.org/10.1016/0550-3213(96)00172-1.0169-68230550-32131873-1562http://nrs.harvard.edu/urn-3:HUL.InstRepos:41385066We construct compact examples of D-manifolds for type IIB strings. The construction has a natural interpretation in terms of compactification of a 12-dimensional 'F-theory'. We provide evidence for a more natural reformulation of type IIB theory in terms of F-theory. Compactification of M-theory on a manifold K which admits elliptic fibration is equivalent to compactification of F-theory on K x S-1. A large class of N = 1 theories in 6 dimensions are obtained by compactification of F-theory on Calabi-Yau threefolds. A class of phenomenologically promising compactifications of F-theory is on Spin(7) holonomy manifolds down to 4 dimensions. This may provide a concrete realization of Witten's proposal for solving the cosmological constant problem in four dimensions.en-USJournal Article2019-09-2210.1016/0550-3213(96)00172-1