RUS  ENG
Full version
JOURNALS // Trudy Instituta Matematiki i Mekhaniki UrO RAN // Archive

Trudy Inst. Mat. i Mekh. UrO RAN, 2021 Volume 27, Number 1, Pages 103–109 (Mi timm1795)

On а question concerning the tensor product of modules

A. V. Konygin

Institute of Mathematics and Mechanics, Ural Branch of the Russian Academy of Sciences, Ekaterinburg

Abstract: Assume that $G$ is a group, $K$ is an algebraically closed field, and $V_1$ and $V_2$ are $KG$-modules. The following question is considered: under what constraints on $G$, $K$, $V_1$, and $V_2$ does $V_1 \otimes V_2 \cong V_1 \otimes I$ hold, where $I$ is the trivial $KG$-module (of dimension $\dim(V_2)$)? Earlier, when considering a problem of P. Cameron on finite primitive permutation groups, the author obtained and used some results on this question. This work continues the study of the question. The following results were obtained. 1. Assume that $G$ is a nontrivial connected reductive algebraic group, and $V_1$ and $V_2$ are faithful semisimple $KG$-modules. Then $V_1 \otimes V_2 \ncong V_1 \otimes I$. 2. Assume that $G$ is a nontrivial finite group, $\mathrm{char} (K) = 0$, $V_1$ is a $KG$-module, and $V_2$ is a faithful $KG$-module. Then $V_1 \otimes V_2 \cong V_1 \otimes I $ if and only if $V_1$ is the direct sum of $\frac {\dim (V_1)} {|G|}$ regular $KG$-modules. In addition, we consider the question of the possibility that $V_1 \otimes V_2 \cong V_1 \otimes I$ in the case where $G = SL_2(p^n)$, $V_1$ and $V_2$ are simple $KG$-modules, and $\mathrm{char}(K) = p$.

Keywords: finite group, algebraic group, group representation, tensor product of modules.

UDC: 512.542, 512.547

MSC: 20C33, 20B15, 20C20, 20D06

Received: 22.11.2020
Revised: 30.12.2020
Accepted: 11.01.2021

DOI: 10.21538/0134-4889-2021-27-1-103-109



Bibliographic databases:


© Steklov Math. Inst. of RAS, 2025