arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1202.6645math.RAcs.DMmath.GR
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关于无挠的群的群环中具有小支撑的零因子

On Zero Divisors with Small Support in Group Rings of Torsion-Free Groups

Pascal Schweitzer

摘要:

Kaplanski的零因子猜想设想,对于无挠的群G和整环R,群环R[G]不包含非平凡的零因子。我们定义R[G]中元素a的长度为最小非负整数k,对于该最小非负整数k,存在环元素r_1,.,R中的r_k和群元素g_1,...,g_k在G中使得a = r_1 g_1+.+ r_k g_k。研究了R是有理数域时的猜想.通过对二元有限域的一个约化,我们证明了:对于有理数上无挠无挠的群的群环中的非平凡元,若ab = 0,则a和b的长度不可能在某些组合中.更确切地说,我们证明了各种对的整数(i,j),如果一个长度是最多i,那么其他长度必须超过j。使用组合参数,我们证明了这对(3,6)和(4,4)。通过计算机辅助的方法,我们加强了这一点,以证明该陈述对(3,16)和(4,7)成立。作为我们的方法的一部分,我们描述了一个组合结构,我们称之为匹配的矩形,并表明,对于这些一个典型的标签可以计算在二次时间。每个匹配的矩形产生一个组的表示。这些相关的群是普遍的,在这个意义上,它们之间没有猜想的反例,当且仅当猜想在有理数上为真。

英文摘要:

Kaplanski's Zero Divisor Conjecture envisions that for a torsion-free group G and an integral domain R, the group ring R[G] does not contain non-trivial zero divisors. We define the length of an element a in R[G] as the minimal non-negative integer k for which there are ring elements r_1,...,r_k in R and group elements g_1,...,g_k in G such that a = r_1 g_1+...+r_k g_k. We investigate the conjecture when R is the field of rational numbers. By a reduction to the finite field with two elements, we show that if ab = 0 for non-trivial elements in the group ring of a torsion-free group over the rationals, then the lengths of a and b cannot be among certain combinations. More precisely, we show for various pairs of integers (i,j) that if one of the lengths is at most i then the other length must exceed j. Using combinatorial arguments we show this for the pairs (3,6) and (4,4). With a computer-assisted approach we strengthen this to show the statement holds for the pairs (3,16) and (4,7). As part of our method, we describe a combinatorial structure, which we call matched rectangles, and show that for these a canonical labeling can be computed in quadratic time. Each matched rectangle gives rise to a presentation of a group. These associated groups are universal in the sense that there is no counterexample to the conjecture among them if and only if the conjecture is true over the rationals.

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