Orbi-Instantons and Class Theories of Type D
arXiv:2602.03931 · doi:10.1007/JHEP06(2026)190
Abstract
We investigate the landscape of 6d D-type orbi-instanton superconformal field theories (SCFTs) and their torus compactifications to four-dimensional class theories. By analysing a general class of 6d F-theory constructions via generalised quivers, we demonstrate that -- in contrast to the well-characterised A-type series -- the dimensional reductions that admit a 4d class description on a Riemann sphere with three untwisted D-type punctures constitute only a subset of the full orbi-instanton landscape. For this subclass, we show that the punctures can be effectively characterised by two sets of integers: the -labels and the -labels. The -labels, or ``Kac-type labels'', serve as the D-type analogues to the Kac labels used in A-type theories; we establish their correspondence with ``modified excess numbers'' in the associated 3d mirror theories (magnetic quivers). The -labels are further introduced to streamline the mapping from 6d generalised quivers to their class descriptions. Furthermore, we analyse physical distinctions arising from 6d angles and explore the hierarchy of Higgs branch flows. In doing so, we uncover instances of ``hidden Higgsings'' -- renormalization group flows present in the 6d parent theories that are not manifest in the puncture closures of the corresponding class descriptions.
73 pages with a number of diagrams and figures. Version 2: Published in JHEP
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