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Recently, the second and third authors introduced a new symmetric tensor category $\underline{\mathrm{Perm}}(G, \mu)$ associated to an oligomorphic group $G$ with a measure $\mu$. When $G$ is the group of order preserving self-bijections of…

Category Theory · Mathematics 2025-10-14 Kevin Coulembier , Nate Harman , Andrew Snowden

Given an oligomorphic group $G$ and a measure $\mu$ for $G$ (in a sense that we introduce), we define a rigid tensor category $\underline{\mathrm{Perm}}(G; \mu)$ of "permutation modules," and, in certain cases, an abelian envelope…

Representation Theory · Mathematics 2024-04-03 Nate Harman , Andrew Snowden

Let $G$ be the group of all order-preserving self-maps of the real line. In previous work, the first two authors constructed a pre-Tannakian category $\underline{\mathrm{Rep}}(G)$ associated to $G$. The present paper is a detailed study of…

Representation Theory · Mathematics 2023-01-09 Nate Harman , Andrew Snowden , Noah Snyder

We extend the calculus of relations to embed a regular category A into a family of pseudo-abelian tensor categories T(A,d) depending on a degree function d. Under the condition that all objects of A have only finitely many subobjects, our…

Category Theory · Mathematics 2007-09-20 Friedrich Knop

The Delannoy category is an interesting pre-Tannakian category associated to the oligomorphic group $\mathbb{G}$ of automorphisms of the totally ordered set $(\mathbf{R}, <)$. By construction, it admits some obvious simple commutative…

Representation Theory · Mathematics 2026-05-19 Pavel Etingof , Andrew Snowden

We introduce some new symmetric tensor categories based on the combinatorics of trees: a discrete family $\mathcal{D}(n)$, for $n \ge 3$ an integer, and a continuous family $\mathcal{C}(t)$, for $t \ne 1$ a complex number. The construction…

Representation Theory · Mathematics 2024-03-19 Nate Harman , Ilia Nekrasov , Andrew Snowden

Let $G$ (resp. $H$) be the group of orientation preserving self-homeomorphisms of the unit circle (resp. real line). In previous work, the first two authors constructed pre-Tannakian categories $\underline{\mathrm{Rep}}(G)$ and…

Representation Theory · Mathematics 2023-03-21 Nate Harman , Andrew Snowden , Noah Snyder

Recently, Harman and the second author introduced a new construction of pre-Tannakian tensor categories based on oligomorphic groups. We develop tools for analyzing the Drinfeld centers of these categories, and compute the center explicitly…

Representation Theory · Mathematics 2026-04-02 Pavel Etingof , Andrew Snowden

Pre-Tannakian categories are a natural class of tensor categories that can be viewed as generalizations of algebraic groups. We define a pre-Tannkian category to be discrete if it is generated by an \'etale commutative algebra; these…

Representation Theory · Mathematics 2023-04-12 Nate Harman , Andrew Snowden

In recent joint work with Harman, we studied a pre-Tannakian category called the Delannoy category, and showed that it had numerous special properties. One of these is that the Adams operations on its Grothendieck group are trivial. In this…

Representation Theory · Mathematics 2025-11-11 Andrew Snowden , Noah Snyder

We prove a constructive existence theorem for abelian envelopes of non-abelian monoidal categories. This establishes a new tool for the construction of tensor categories. As an example we obtain new proofs for the existence of several…

Category Theory · Mathematics 2023-06-22 Kevin Coulembier

The principal aim of this note is to give an elementary proof of the fact that any two fiber functors of a Tannakian category are locally isomorphic. This builds on an idea of Deligne concerning scalar extensions of Tannakian categories and…

Algebraic Geometry · Mathematics 2018-05-10 Daniel Schäppi

Let $\mathcal{C}$ be an additive category. The nilpotent category $\mathrm{Nil} (\mathcal{C})$ of $\mathcal{C}$, consists of objects pairs $(X, x)$ with $X\in\mathcal{C}, x\in\mathrm{End}_{\mathcal{C}}(X)$ such that $x^n=0$ for some…

Category Theory · Mathematics 2021-11-30 Zhiwei Bai , Xiang Cao , Songtao Mao , Han Zhang , Yuehui Zhang

We prove an analog of Deligne's theorem for finite symmetric tensor categories $\mathcal{C}$ with the Chevalley property over an algebraically closed field $k$ of characteristic $2$. Namely, we prove that every such category $\mathcal{C}$…

Quantum Algebra · Mathematics 2019-12-03 Pavel Etingof , Shlomo Gelaki

We study abelian envelopes for pseudo-tensor categories with the property that every object in the envelope is a quotient of an object in the pseudo-tensor category. We establish an intrinsic criterion on pseudo-tensor categories for the…

Category Theory · Mathematics 2022-10-18 Kevin Coulembier , Pavel Etingof , Victor Ostrik , Bregje Pauwels

We give several criteria to decide whether a given tensor category is the abelian envelope of a fixed symmetric monoidal category. As a main result we prove that the category of finite-dimensional representations of a semisimple simply…

Representation Theory · Mathematics 2022-12-21 Kevin Coulembier , Inna Entova-Aizenbud , Thorsten Heidersdorf

A Tannakian category is an abelian tensor category equipped with a fiber functor and additional structures which ensure that it is equivalent to the category of representations of some affine groupoid scheme acting on the spectrum of a…

Category Theory · Mathematics 2018-05-10 Daniel Schäppi

For a large class of geometric objects, the passage to categories of quasi-coherent sheaves provides an embedding in the 2-category of abelian tensor categories. The notion of weakly Tannakian categories introduced by the author gives a…

Algebraic Geometry · Mathematics 2018-05-10 Daniel Schäppi

We study stabilization of finite-dimensional representations of the periplectic Lie superalgebras $\mathfrak{p}(n)$ as $n \to \infty$. The paper gives a construction of the tensor category $Rep(\underline{P})$, possessing nice universal…

Representation Theory · Mathematics 2019-12-10 Inna Entova-Aizenbud , Vera Serganova

The principle of tannakian duality states that any neutral tannakian category is tensorially equivalent to the category Rep_k G of finite dimensional representations of some affine group scheme G and field k, and conversely. Originally…

Representation Theory · Mathematics 2010-11-03 Michael Crumley
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