Categorical Webs and $S$-duality in 4d $\mathcal{N}=2$ QFT

Understand

We review the categorical approach to the BPS sector of a 4d $\mathcal{N}=2$ QFT, clarifying many tricky issues and presenting a few novel results.

• To a given $\mathcal{N}=2$ QFT one associates several triangle categories: they describe various kinds of BPS objects from different physical viewpoints (e.g.
• IR versus UV).
• These diverse categories are related by a web of exact functors expressing physical relations between the various objects/pictures.