Kochetov's PI conjecture for smash products of hyperalgebras

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Let HH be a hyperalgebra over a perfect field F\mathbb{F}. If char⁡F>0\operatorname{char}\mathbb{F}>0, assume also that HH is reduced. Let GG be a group acting on HH by bialgebra automorphisms.

Kochetov's conjecture. The smash product H#FGH\#\mathbb{F}G is PI if and only if

(i)H is commutative;(ii)there exist normal subgroups G0⊂G1⊂G such that G/G1 is finite,G1/G0 is abelian, and G0 is a finite p-group if char⁡F=p>0and trivial if char⁡F=0;(iii)G1 acts trivially on H.\begin{array}{ll} \text{(i)} & H\text{ is commutative};\\ \text{(ii)} & \text{there exist normal subgroups }G_0\subset G_1\subset G\text{ such that }G/G_1\text{ is finite},\\ & G_1/G_0\text{ is abelian, and }G_0\text{ is a finite }p\text{-group if }\operatorname{char}\mathbb{F}=p>0\\ & \text{and trivial if }\operatorname{char}\mathbb{F}=0;\\ \text{(iii)} & G_1\text{ acts trivially on }H. \end{array}

This conjecture proposes a complete PI criterion for smash products of connected Hopf algebras by combining commutativity of the hyperalgebra with a finite-by-abelian structure condition on the acting group. The statement extends known criteria for enveloping algebras, restricted enveloping algebras, and group algebras, but the general case remains open.

References

Primary source

Yuri Bahturin and Sarah Witherspoon, “Delta sets and polynomial identities in pointed Hopf algebras”, arXiv:2101.09767 (2021).

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