Kochetov's PI conjecture for smash products of hyperalgebras

Let HH be a hyperalgebra over a perfect field F\mathbb{F}. If charF>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 G0G1G such that G/G1 is finite,G1/G0 is abelian, and G0 is a finite p-group if charF=p>0and trivial if charF=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.

Sources & referencesView supporting material

Primary source

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

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