Abstract:
In this talk, I will discuss weakly-coupled descriptions of the typically non-Lagrangian 4d N=2 theories of class S, from the perspective of the 3d N=4 mirror duals of their circle compactifications. These descriptions often produce pathological configurations which I will relate to a corresponding notion of "badness" in the 3d N=4 theories. Leveraging some recent results regarding these 3d bad theories, I will introduce a new class of theories - broken theories - that naturally emerge in this setting. Building on these, I will present the systematic and analytic method that we have developed to determine the non-Lagrangian matter sectors and the weakly-coupled gauge groups in these frames, which arise dynamically via Higgsings triggered by operator vevs.