On braided simple extensions and braided non-semisimple near-group categories (2512.12556v1)

Abstract: Let $\mathcal{C}$ be a finite tensor category with a decomposition $\mathcal{C}\cong \mathcal{D}\oplus{\mathcal{M}}$ into full abelian categories such that $\mathcal{D}$ is a tensor subcategory and $\mathcal{M}$ has a single simple projective object. We call $\mathcal{C}$ a simple extension of $\mathcal{D}$. When $\mathcal{C}$ is braided and $\mathcal{D}$ is a braided subcategory, we will call $\mathcal{C}$ a braided simple extension. Applying the notion of a simple extension to a pointed non-semisimple category $\mathcal{D}$ gives a natural generalization to the family of near-group categories, which was first introduced by Siehler. Braided near-group categories were fully classified by Siehler and Thornton. In this paper, we study the structure of braided simple extensions of a braided finite tensor category $\mathcal{D}$ in general, and specifically when $\mathcal{D}$ is pointed. In particular, we classify non-degenerate braided non-semisimple near-group categories, and prove that any braided non-semisimple near-group category $\mathcal{C}$ is "an extension" of a non-degenerate braided non-semisimple near-group category by $Rep(G)$, where $G$ is the Picard group of a "canonical" symmetric subcategory of $\mathcal{C}$.