English

Hopf $2$-cocycles for certain affine algebraic reductive groups

Representation Theory 2026-07-21 v1 Quantum Algebra

Abstract

Motivated by the open problem of classifying Hopf 22-cocycles for affine algebraic reductive groups GG over C\mathbb{C}, in particular by \cite[Question 7.2]{EG1} which concerns minimal Hopf 22-cocycles, we classify (minimal) Hopf 22-cocycles for affine algebraic reductive groups GG whose connected component of the identity is a torus TT. To achieve this we utilize \cite[Proposition 5.4]{ENO} in our situation to classify finite indecomposable semisimple module categories over the infinite semisimple equivariantization tensor category \Rep(T)K\Rep(G)\Rep(T)^K\simeq \Rep(G), where K:=G/TK:=G/T. We then use it to classify the module categories over \Rep(G)\Rep(G) of rank 11, and show that the corresponding fiber functors on \Rep(G)\Rep(G) are classical (that is, preserve dimensions), which implies that they are in bijection with Hopf 22-cocycles for GG.

Cite

@article{arxiv.2607.18599,
  title  = {Hopf $2$-cocycles for certain affine algebraic reductive groups},
  author = {Shlomo Gelaki},
  journal= {arXiv preprint arXiv:2607.18599},
  year   = {2026}
}

Comments

25 pages