Heterotic/$F$-theory duality and Narasimhan–Seshadri equivalence

Finding the $F$-theory dual of a Heterotic model with Wilson-line symmetry breaking presents the challenge of achieving the dual $\mathbb{Z}_{2}$-action on the $F$-theory model in such a way that the $\mathbb{Z}_{2}$-quotient is Calabi-Yau with an Enriques $\mathrm{GUT}$ surface over which $SU\left(5\right)_{gauge}$ symmetry is maintained. We propose a new way to approach this problem by taking advantage of a little-noticed choice in the application of Narasimhan-Seshadri equivalence between real $E_{8}$-bundles with Yang-Mills connection and their associated complex holomorphic $E_{8}^{\mathbb{C}}$-bundles, namely the one given by the real outer automorphism of $E_{8}^{\mathbb{C}}$ by complex conjugation. The triviality of the restriction on the compact real form $E_{8}$ allows one to introduce it into the $\mathbb{Z}_{2}$-action, thereby restoring $E_{8}$- and hence $SU\left(5\right)_{gauge}$ -symmetry on which the Wilson line can be wrapped.