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arXiv 1203.5232math.RAmath.ACmath.GRmath.KT
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整群环的中心单位

Central units of integral group rings

Eric Jespers, Gabriela Olteanu, Ángel del Río, Inneke Van Gelder

摘要:

给出了有限阿贝尔超可解群的整群环$\Z G$的中心单元群中有限指数子群的基的显式描述,使得每个阶不是4或6的因子的循环子群在$G$中是次正规的。基元是Bass单位共轭的自然产物。这推广了Jespers,Parmenter和Sehgal的一个结果:当$G$是有限幂零群时,Bass单位在单位群$\U (\Z G)$的中心$\mathcal{Z} (\U (\Z G))$生成一个指数有限的子群.其次,我们给出了一种新的单位的构造,该单位在$\mathcal{Z}(\U(\Z G))$中生成一个有限指数的子群,对于所有有限强单项式群$G$。我们称这些单位为广义巴斯单位。最后,证明了交换子群$\U(\Z G)/\U(\Z G)'$和$\mathcal{Z}(\U(\Z G))$具有相同的秩,如果$G$是一个有限群,使得$\Q G$没有满射像,它不是一个全定四元数代数,也不是一个以$\Q$的有理数或二次虚扩张为中心的除代数上的二乘二矩阵代数.这使我们能够证明,在这种情况下,自然图像的低音单位的$\Z G$生成一个子群的有限指数在$\U(\Z G)/\U(\Z G)'$。

英文摘要:

We give an explicit description for a basis of a subgroup of finite index in the group of central units of the integral group ring $\Z G$ of a finite abelian-by-supersolvable group such that every cyclic subgroup of order not a divisor of 4 or 6 is subnormal in $G$. The basis elements turn out to be a natural product of conjugates of Bass units. This extends and generalizes a result of Jespers, Parmenter and Sehgal showing that the Bass units generate a subgroup of finite index in the center $\mathcal{Z} (\U (\Z G))$ of the unit group $\U (\Z G)$ in case $G$ is a finite nilpotent group. Next, we give a new construction of units that generate a subgroup of finite index in $\mathcal{Z}(\U(\Z G))$ for all finite strongly monomial groups $G$. We call these units generalized Bass units. Finally, we show that the commutator group $\U(\Z G)/\U(\Z G)'$ and $\mathcal{Z}(\U(\Z G))$ have the same rank if $G$ is a finite group such that $\Q G$ has no epimorphic image which is either a non-commutative division algebra other than a totally definite quaternion algebra, or a two-by-two matrix algebra over a division algebra with center either the rationals or a quadratic imaginary extension of $\Q$. This allows us to prove that in this case the natural images of the Bass units of $\Z G$ generate a subgroup of finite index in $\U(\Z G)/\U(\Z G)'$.

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