Even More On Twisted $A_{2n}$ Class-S Theories

Abstract: This paper is a continuation of our investigation into the Coulomb branches of twisted $A_{2n}$ of class-S. In arXiv:2411.17675, we found predictions for the contributions of twisted punctures to the graded dimensions of the Coulomb branch, based on the behaviour under nilpotent Higgsings and S-duality. While surprisingly powerful, these arguments were indirect. Here, we take a different approach: we define precisely the nature of the automorphism under which the twisted punctures are twisted (in particular, it is order-4, not order-2). From that, we find the local constraints satisfied by the Laurent coefficients of the invariant polynomials in the Higgs field, for all twisted punctures in $A_{2n}$, for all n. A crucial role is played by a new (at least, new in physics) order-reversing map on the set of nilpotent orbits in sp(n). Finally, we construct several examples of Seiberg-Witten curves for 3-punctured spheres in these theories.