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Semigroup graded algebras and graded PI-exponent

机译:半群分级代数和分级 PI 指数

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Let S be a semigroup. We study the structure of graded-simple S-graded algebras A and the exponential rate PIexp (S-gr)(A):= lim(n -> a) of growth of codimensions c (n) (S-gr) (A) of their graded polynomial identities. This is of great interest since such algebras can have non-integer PIexp (S-gr)(A) despite being finite dimensional and associative. In addition, such algebras can have a non-trivial Jacobson radical J(A). All this is in strong contrast with the case when S is a group since in the group case J(A) is trivial, PIexp (S-gr)(A) is always integer and, if the base field is algebraically closed, then PIexp (S-gr)(A) equals dimA. Without any restrictions on the base field F, we classify graded-simple S-graded algebras A for a class of semigroups S which is complementary to the class of groups. We explicitly describe the structure of J(A) showing that J(A) is built up of pieces of a maximal S-graded semisimple subalgebra of A which turns out to be simple. When F is algebraically closed, we get an upper bound for . If A/J(A) ae M (2)(F) and S is a right zero band, we show that this upper bound is sharp and PIexp (S-gr)(A) indeed exists. In particular, we present an infinite family of graded-simple algebras A with arbitrarily large non-integer PIexp (S-gr)(A).
机译:设 S 为半群。我们研究了梯度简单 S 梯度代数 A 的结构及其渐变多项式恒等式的协维 c (n) (S-gr) (A) 增长的指数速率 PIexp (S-gr)(A):= lim(n -> a)。这引起了人们的极大兴趣,因为尽管这些代数是有限维数和关联的,但可以具有非整数 PIexp (S-gr)(A)。此外,这样的代数可以有一个非平凡的雅各布森根式J(A)。所有这些都与 S 是一个群的情况形成鲜明对比,因为在群的情况下,J(A) 是平凡的,PIexp (S-gr)(A) 总是整数,如果基域是代数闭合的,则 PIexp (S-gr)(A) 等于 dimA。在对基域 F 没有任何限制的情况下,我们将分级简单 S 分级代数 A 分类为一类半群 S,该半群 S 与群类互补。我们明确地描述了 J(A) 的结构,表明 J(A) 是由 A 的最大 S 级半简单子代数的片段组成的,结果证明是简单的。当 F 以代数闭合方式闭合时,我们得到 的上限。如果 A/J(A) ae M (2)(F) 和 S 是右零波段,我们证明这个上限是尖锐的,并且 PIexp (S-gr)(A) 确实存在。特别是,我们提出了一个具有任意大非整数 PIexp (S-gr)(A) 的无穷高分阶简单代数 A 族。

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