M5-instanton corrections to the superpotential in four-dimensional F-theory compactifications have a moduli-dependent prefactor which contains interesting physical content. In two examples obtained via heterotic duality, I will show that the entire vanishing locus of the prefactor can be understood via simple F-theory physics, often occurring at enhanced symmetry points in the complex structure moduli space. If time permits, I will discuss the relationship between line bundle cohomology on a distinguished curve in the instanton worldvolume and the intermediate Jacobian of the M5-instanton.
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