English

Smoothness of commutative Hopf algebras

Rings and Algebras 2025-10-14 v3 Algebraic Geometry

Abstract

Hopf algebras, most generally in a semisimple abelian symmetric monoidal category, are here supposed to be commutative but not to be of finite-type, and their (equivariant) smoothness are discussed. Given a Hopf algebra HH in a category such as above, it is proved that the following are equivalent: (i) HH is smooth as an algebra; (ii) HH is smooth as an HH-comodule algebra; (iii) the product morphism SH2(H+)H+S_H^2(H^+) \to H^+ defined on the 2nd symmetric power is monic. Working over a field kk of characteristic zero, we prove: (1) every ordinary Hopf algebra, i.e., such in the category Vec\mathsf{Vec} of vector spaces, satisfies the equivalent conditions (i)--(iii) and some others; (2) every Hopf algebra in the category sVec\mathsf{sVec} of super-vector spaces has a certain property that is stronger than (i). In the case where chark=p>0\operatorname{char}k=p>0, there are shown weaker properties of ordinary Hopf algebras and of Hopf algebras in sVec\mathsf{sVec} or in the ind-completion Verpind\mathsf{Ver}_p^{\mathrm{ind}} of the Verlinde category.

Keywords

Cite

@article{arxiv.2412.19038,
  title  = {Smoothness of commutative Hopf algebras},
  author = {Kensuke Egami and Akira Masuoka and Kenta Suzuki},
  journal= {arXiv preprint arXiv:2412.19038},
  year   = {2025}
}

Comments

Corrected typos, added more details to several places