Nichols algebras, tensor categories and Kazhdan-Lusztig correspondences

Abstract

There is a very general picture emerging that conjecturally describes what happens to the representation theory of a vertex algebra $\mathcal{V}$ if we pass to the kernel $\mathcal{W}$ of a set of screening operators. Namely, the screening operators generate a Nichols algebra $H$ inside $\mathrm{Rep}(\mathcal{V})$ and in many cases $\mathrm{Rep}(\mathcal{W})$ coincides with the relative Drinfeld center of $\mathrm{Rep}(H)$. This vastly generalizes the construction of a quantum group as the Drinfeld double of a Nichols algebra over the Cartan part. In this example, the conjectural category equivalence has been studied since around $20$ years as logarithmic Kazhdan Lusztig correspondence. The present survey was part of my habilitation thesis about my work in this area. I want to make it available as an introductory text, intended for readers from a pure algebra background as well as from a physics background. I motivate and explain gently and informally the different topics involved (quantum groups, Nichols algebras, vertex algebras, braided tensor categories) with a distinct categorical point of view, to the point that I can explain my general expectation. Then I explain some previous results and explain the main techniques in my recent proof of the conjectured category equivalence in case $\mathcal{V}$ is a free field theory and under technical assumptions on the analysis side.