Magnetic quivers and negatively charged branes

The Higgs branches of the world-volume theories for multiple M5 branes on an $A_k$ or $D_k$-type ALE space are known to host a variety of fascinating properties, such as the small $E_8$ instanton transition or the discrete gauging phenomena. This setup can be further enriched by the inclusion of boundary conditions, which take the form of $SU(k)$ or $SO(2k)$ partitions, respectively. Unlike the $A$-type case, $D$-type boundary conditions are eventually accompanied by negative brane numbers in the Type IIA brane realisation. While this may seem discouraging at first, we demonstrate that these setups are well-suited to analyse the Higgs branches via magnetic quivers. Along the way, we encounter multiple models with previously neglected Higgs branches that exhibit exciting physics and novel geometric realisations. Nilpotent orbits, Slodowy slices, and symmetric products.