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Group gradings on associative algebras. (English) Zbl 0988.16033

Let \(G\) be a group, \(S=M_n(D)\) the \(n\times n\) matrix ring over a division ring \(D\), and \(E_{ij}\), \(1\leq i,j\leq n\), the matrix units. A grading \(S=\bigoplus_{g\in G}S_g\) on the ring \(S\) is called elementary if there exists a set \((g_1,\dots,g_n)\in G^n\) such that \(E_{ij}\in S_g\Leftrightarrow g=g_i^{-1}g_j\), and \(D\subseteq S_e\). A result of M. V. Zaicev and S. K. Sehgal [Mosc. Univ. Math. Bull. 56, No. 3, 21-24 (2001); translation from Vestn. Mosk. Univ., Ser. I 2001, No. 3, 21-25 (2001; Zbl 1054.16032)] asserts that any simple Artinian ring \(R=\bigoplus_{g\in G}R_g\) with a finite \(G\)-grading by a torsion-free group \(G\) is isomorphic as graded ring to a matrix ring \(M_n(D)\) with an elementary \(G\)-grading. In the present paper, using this result the authors give a complete description of all types of finite gradings on a semisimple Artinian ring if the grading group is torsion-free. If \(R\) is a matrix algebra over an algebraically closed field \(F\) and \(G\) is an Abelian group they describe all \(G\)-gradings on \(R\). In the case of an Abelian group \(G\) they also classify all finite dimensional graded simple algebras and finite dimensional graded division algebras over an algebraically closed field of characteristic zero.

MSC:

16W50 Graded rings and modules (associative rings and algebras)
16S50 Endomorphism rings; matrix rings
16K20 Finite-dimensional division rings
16P10 Finite rings and finite-dimensional associative algebras
16P20 Artinian rings and modules (associative rings and algebras)

Citations:

Zbl 1054.16032

References:

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