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String and 5-brane junctions are shown to succinctly classify all known 8D N=1 string vacua. This requires an extension of the description for ordinary p, q-7-branes to consistently include O7^+ planes, which then naturally encodes the dynamics of sp₍ gauge algebras, including their p-form center symmetries. Central to this analysis are loop junctions, i. e. , strings/5-branes which encircle stacks of 7-branes and O7^+s. Loop junctions further signal the appearance of affine symmetries of emergent 9D descriptions at the 8D moduli space's boundaries. Such limits reproduce all 9D string vacua, including the two disconnected rank (1, 1) moduli components.
Cvetič et al. (Thu,) studied this question.