scholarly journals $p$-adic dimensions in symmetric tensor categories in characteristic $p$

2018 ◽  
Vol 9 (1) ◽  
pp. 119-140 ◽  
Author(s):  
Pavel Etingof ◽  
Nate Harman ◽  
Viktor Ostrik
Keyword(s):  
Symmetric Tensor ◽  
Characteristic P ◽  
Tensor Categories

scholarly journals Finite Symmetric Integral Tensor Categories with the Chevalley Property with an Appendix by Kevin Coulembier and Pavel Etingof

2019 ◽  
Author(s):  
Pavel Etingof ◽  
Shlomo Gelaki
Keyword(s):  
Hopf Algebras ◽  
Tensor Category ◽  
Group Scheme ◽  
Symmetric Tensor ◽  
Closed Field ◽  
Characteristic P ◽  
Tensor Categories ◽  
Algebraically Closed Field ◽  
Finite Dimensional ◽  
Chevalley Property

Abstract We prove that every finite symmetric integral tensor category $\mathcal{C}$ with the Chevalley property over an algebraically closed field $k$ of characteristic $p>2$ admits a symmetric fiber functor to the category of supervector spaces. This proves Ostrik’s conjecture [25, Conjecture 1.3] in this case. Equivalently, we prove that there exists a unique finite supergroup scheme $\mathcal{G}$ over $k$ and a grouplike element $\epsilon \in k\mathcal{G}$ of order $\le 2$, whose action by conjugation on $\mathcal{G}$ coincides with the parity automorphism of $\mathcal{G}$, such that $\mathcal{C}$ is symmetric tensor equivalent to $\textrm{Rep}(\mathcal{G},\epsilon )$. In particular, when $\mathcal{C}$ is unipotent, the functor lands in $\textrm{Vec}$, so $\mathcal{C}$ is symmetric tensor equivalent to $\textrm{Rep}(U)$ for a unique finite unipotent group scheme $U$ over $k$. We apply our result and the results of [17] to classify certain finite dimensional triangular Hopf algebras with the Chevalley property over $k$ (e.g., local), in group scheme-theoretical terms. Finally, we compute the Sweedler cohomology of restricted enveloping algebras over an algebraically closed field $k$ of characteristic $p>0$, classify associators for their duals, and study finite dimensional (not necessarily triangular) local quasi-Hopf algebras and finite (not necessarily symmetric) unipotent tensor categories over an algebraically closed field $k$ of characteristic $p>0$. The appendix by K. Coulembier and P. Etingof gives another proof of the above classification results using the recent paper [4], and more generally, shows that the maximal Tannakian and super-Tannakian subcategory of a symmetric tensor category over a field of characteristic $\ne 2$ is always a Serre subcategory.

scholarly journals Symmetric tensor categories in characteristic 2

2019 ◽  
Vol 351 ◽  
pp. 967-999 ◽  
Author(s):  
Dave Benson ◽  
Pavel Etingof
Keyword(s):  
Symmetric Tensor ◽  
Tensor Categories ◽  
Characteristic 2

scholarly journals On the Frobenius functor for symmetric tensor categories in positive characteristic

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Pavel Etingof ◽  
Victor Ostrik
Keyword(s):  
Positive Characteristic ◽  
Symmetric Tensor ◽  
Tensor Categories ◽  
Large Power ◽  
Exact Category ◽  
Fusion Categories ◽  
Moderate Growth ◽  
Monoidal Functor ◽  
New Feature ◽  
The One

AbstractWe develop a theory of Frobenius functors for symmetric tensor categories (STC) {\mathcal{C}} over a field {\boldsymbol{k}} of characteristic p, and give its applications to classification of such categories. Namely, we define a twisted-linear symmetric monoidal functor {F:\mathcal{C}\to\mathcal{C}\boxtimes{\rm Ver}_{p}}, where {{\rm Ver}_{p}} is the Verlinde category (the semisimplification of {\mathop{\mathrm{Rep}}\nolimits_{\mathbf{k}}(\mathbb{Z}/p)}); a similar construction of the underlying additive functor appeared independently in [K. Coulembier, Tannakian categories in positive characteristic, preprint 2019]. This generalizes the usual Frobenius twist functor in modular representation theory and also the one defined in [V. Ostrik, On symmetric fusion categories in positive characteristic, Selecta Math. (N.S.) 26 2020, 3, Paper No. 36], where it is used to show that if {\mathcal{C}} is finite and semisimple, then it admits a fiber functor to {{\rm Ver}_{p}}. The main new feature is that when {\mathcal{C}} is not semisimple, F need not be left or right exact, and in fact this lack of exactness is the main obstruction to the existence of a fiber functor {\mathcal{C}\to{\rm Ver}_{p}}. We show, however, that there is a 6-periodic long exact sequence which is a replacement for the exactness of F, and use it to show that for categories with finitely many simple objects F does not increase the Frobenius–Perron dimension. We also define the notion of a Frobenius exact category, which is a STC on which F is exact, and define the canonical maximal Frobenius exact subcategory {\mathcal{C}_{\rm ex}} inside any STC {\mathcal{C}} with finitely many simple objects. Namely, this is the subcategory of all objects whose Frobenius–Perron dimension is preserved by F. One of our main results is that a finite STC is Frobenius exact if and only if it admits a (necessarily unique) fiber functor to {{\rm Ver}_{p}}. This is the strongest currently available characteristic p version of Deligne’s theorem (stating that a STC of moderate growth in characteristic zero is the representation category of a supergroup). We also show that a sufficiently large power of F lands in {\mathcal{C}_{\rm ex}}. Also, in characteristic 2 we introduce a slightly weaker notion of an almost Frobenius exact category (namely, one having a fiber functor into the category of representations of the triangular Hopf algebra {\boldsymbol{k}[d]/d^{2}} with d primitive and R-matrix {R=1\otimes 1+d\otimes d}), and show that a STC with Chevalley property is (almost) Frobenius exact. Finally, as a by-product, we resolve Question 2.15 of [P. Etingof and S. Gelaki, Exact sequences of tensor categories with respect to a module category, Adv. Math. 308 2017, 1187–1208].

scholarly journals Finite symmetric tensor categories with the Chevalley property in characteristic 2

2020 ◽  
pp. 2140010
Author(s):  
Pavel Etingof ◽  
Shlomo Gelaki
Keyword(s):  
Tensor Category ◽  
Group Scheme ◽  
Symmetric Tensor ◽  
Function Algebra ◽  
Equivalence Classes ◽  
Closed Field ◽  
Arbitrary Field ◽  
Tensor Categories ◽  
Characteristic 2 ◽  
Chevalley Property

We prove an analog of Deligne’s theorem for finite symmetric tensor categories [Formula: see text] with the Chevalley property over an algebraically closed field [Formula: see text] of characteristic [Formula: see text]. Namely, we prove that every such category [Formula: see text] admits a symmetric fiber functor to the symmetric tensor category [Formula: see text] of representations of the triangular Hopf algebra [Formula: see text]. Equivalently, we prove that there exists a unique finite group scheme [Formula: see text] in [Formula: see text] such that [Formula: see text] is symmetric tensor equivalent to [Formula: see text]. Finally, we compute the group [Formula: see text] of equivalence classes of twists for the group algebra [Formula: see text] of a finite abelian [Formula: see text]-group [Formula: see text] over an arbitrary field [Formula: see text] of characteristic [Formula: see text], and the Sweedler cohomology groups [Formula: see text], [Formula: see text], of the function algebra [Formula: see text] of [Formula: see text].

Sign in / Sign up

Export Citation Format

Share Document