During the past three decades fundamental progress has been made on constructing large torsion-free subgroups (i.e. subgroups of finite index) of the unit group $\U (\Z G)$ of the integral group ring $\Z G$ of a finite group $G$. These constructions rely on explicit constructions of units in $\Z G$ and proofs of main results make use of the description of the Wedderburn components of the rational group algebra $\Q G$. The latter relies on explicit constructions of primitive central idempotents and the rational representations of $G$. It turns out that the existence of reduced two degree representations play a crucial role. Although the unit group is far from being understood, some structure results on this group have been obtained. In this paper we give a survey of some of the fundamental results and the essential needed techniques.
We gather some classical results and examples that show strict inclusion between the families of unital rings, rings with enough idempotents, rings with sets of local units, locally unital rings, s-unital rings and idempotent rings.
Let $R$ be an associative ring with identity and let $N$ be a nil ideal of $R$. It is shown that units of $R/N$ can be lifted to units in $R$. Under some mild conditions on the ring, a procedure is given to determine those lifted units in a recursive way. As an application, the units of several classes of rings are determined, including: matrix rings, chain rings, and group rings where the ring is a chain ring. Numerical examples are given illustrating the main results.
We extend the classical construction by Noether of crossed product algebras, defined by finite Galois field extensions, to cover the case of separable (but not necessarily finite or normal) field extensions. This leads us naturally to consider non-unital groupoid graded rings of a particular type that we call object unital. We determine when such rings are strongly graded, crossed products, skew groupoid rings and twisted groupoid rings. We also obtain necessary and sufficient criteria for when object unital groupoid graded rings are separable over their principal component, thereby generalizi…
We offer two comments on the beautiful papers of Giles Gardam and Alan Murray that yield counterexamples to the Kaplansky unit conjecture. First we discuss the determinants of these units in a certain $4\times 4$ matrix representation of the group ring. Then we explain why there is a doubly infinite family of units in the Murray paper.
Let $R$ be a finite unitary ring such that $R=R_0[R^*]$ where $R_0$ is the prime ring and $R^*$ is not a nilpotent group. We show that if all proper subgroups of $R^*$ are nilpotent groups, then the cardinal of $R$ is a power of prime number 2. In addition, if $(R/Jac(R))^*$ is not a $p-$group, then either $R\cong M_2(GF(2))$ or $R\cong M_2(GF(2))\oplus A$ where $M_2(GF(2))$ is the ring of $2\times 2$ matrices over the finite field $GF(2)$ and $A$ is a direct sum of finite field $GF(2)$.
The augmentation powers in an integral group ring $\mathbb ZG$ induce a natural filtration of the unit group of $\mathbb ZG$ analogous to the filtration of the group $G$ given by its dimension series $\{D_n(G)\}_{n\ge 1}$. The purpose of the present article is to investigate this filtration, in particular, the triviality of its intersection.
A ring is said to satisfy the $2$-nil-sum property if every non central-unit is the sum of two nilpotents. We prove that a ring satisfies the $2$-nil-sum property iff it is either a simple ring with the $2$-nil-sum property or a commutative local ring with nil Jacobson radical, and we provide an example of a simple ring with the $2$-nil-sum property that is not commutative. Moreover, a simple right Goldie ring has the $2$-nil-sum property iff it is a field.
Let R be a unit-regular ring, and let a,b,c in R satisfy aba=aca. If ac and ba are group invertible, we prove that ac is similar to ba. Furthermore, if ac and ba are Drazin invertible, then their Drazin inverses are similar. For any n\times n complex matrices A,B,C with ABA = ACA ,we prove that AC and BA are similar if and only if their k-powers have the same rank. These generalize the known Flanders' theorem proved by Hartwig.
Let $G$ be a group and let $S=\bigoplus_{g \in G} S_g$ be a $G$-graded ring. Given a normal subgroup $N$ of $G$, there is a naturally induced $G/N$-grading of $S$. It is well-known that if $S$ is strongly $G$-graded, then the induced $G/N$-grading is strong for any $N$. The class of epsilon-strongly graded rings was recently introduced by Nystedt, Öinert and Pinedo as a generalization of unital strongly graded rings. We give an example of an epsilon-strongly graded partial skew group ring such that the induced quotient group grading is not epsilon-strong. Moreover, we give necessary and suffic…
Two questions of L. Va${\rm \check{\textbf{s}}}$ on *-clean rings
一个具有对合 * 的环$R$称为（强）*-clean，如果$R$的每个元素都是单位元与投影（可交换的）之和.所有的戒指都是干净的。Va ${\rm \check{s}}$ [L. Va ${\rm \check{s}}$，*-Clean rings; some clean and almost clean Baer *-rings and von Neumann algebras，J. Algebra 324（12）（2010）3388-3400]询问是否存在干净但不干净的 *-环以及单位正则和 *-正则环是否强 *-clean。在本文中，我们回答这两个问题的几个例子。此外，还给出了单位正则环和 *-正则环的一些刻划.
When does an infinite ring have a finite compressed commuting graph?
University of Banja Luka（班贾卢卡大学）；University of Ljubljana, School of Economics and Business（卢布尔雅那大学经济商学院）；Institute of Mathematics, Physics and Mechanics（数学、物理和力学研究所）；University of Ljubljana, Faculty of Civil and Geodetic Engineering（卢布尔雅那大学土木与测量工程学院）；University of Ljubljana, Faculty of Mathematics and Physics（卢布尔雅那大学数学与物理学院）
We begin by introducing an algebraic structure with three constants and one ternary operation to which we call mobi algebra. This structure has been designed to capture the most relevant properties of the unit interval that are needed in the study of geodesic paths. Another algebraic structure, called involutive medial monoid (IMM), can be derived from a mobi algebra. We prove several results on the interplay between mobi algebras, IMM algebras and unitary rings. It turns out that every unitary ring with one half uniquely determines and is uniquely determined by a mobi algebra with one double.…
*-Clean Rings; Some Clean and Almost Clean Baer *-rings and von Neumann Algebras
戒指是干净的（resp。几乎干净），如果它的每个元素都是一个单位的总和（分别是）。正则元素）和幂等元。在本文中，我们定义了类似的概念，*-环：一个 *-环是 *-干净的（分别）。almost *-clean），如果它的每个元素都是一个单位的和（分别是规则元素）和投影。虽然 *-clean是一个比clean更强的概念，但对于某些 *-环，我们证明它更自然。单位正则环的清洁性定理[V. P. Camillo，D. Khurana，A Characterization of Unit正则环，Communications in Algebra，29（5）（2001）2293-2295]被修改为阿贝尔（或约化或Armendariz）的 *-正则环的 *-清洁性。利用这个结果，证明了所有满足某些公理的有限的I型Baer *-环（在[S. K. Berberian，Baer *-rings，Die Grundlehren der mathematischen Wissenschaften 195，Springer-Verlag，Berlin-Heidelberg-New York，1972]和[L. Vas，Dimension and Torsion Theories for a Class of Baer *-Rings，Journal of Algebra，289（2）（2005）614-6…
On the torsion units of the integral group ring of finite projective special linear groups
H. J.Zassenhaus证明了有限群$G$的整群环中的任意有穷级增广单位在有理群代数中共轭于$G$的一个元素。验证这一点的一种方法是证明这样的单元具有与$G$的元素相同的部分增广分布，并且HeLP方法在某些情况下提供了这样做的工具。本文用HeLP方法描述了关于特殊线性群的猜想的一个假设反例的部分扩充。
The purpose of this paper is to give a partial positive answer to a question raised by Khurana et al. as to whether a ring $R$ with stable range one and central units is commutative. We show that this is the case under any of the following additional conditions: $R$ is semiprime or $R$ is one-sided Noetherian or $R$ has unit-stable range $1$ or $R$ has classical Krull dimension $0$ or $R$ is an algebra over a field $K$ such that $K$ is uncountable and $R$ has only countably many primitive ideals or $R$ is affine and either $K$ has characteristic $0$ or has infinite transcendental degree over i…
Let R be a unitary ring of finite cardinality P^k, where p is a prime number and $p\nmid k$. We show that if the group of units of $R$ has at most one subgroup of order $p$, then $R\cong A\bigoplus B,$ where $B$ is a finite ring of order $k$ and $A$ is a ring of cardinality $p^β$ which is one of the six explicitly described types.
We show that the units found in torsion-free group rings by Gardam are twisted unitary elements. This justifies some choices in Gardam's construction that might have appeared arbitrary, and yields more examples of units. We note that all units found up to date exhibit non-trivial symmetry.
The aim of this article is to draw attention towards various natural but unanswered questions related to the lower central series of the unit group of an integral group ring.
Let $RG$ be the gruop ring of the group $G$ over ring $R$ and $\mathscr{U}(RG)$ be its unit group. Finding the structure of the unit group of a finite group ring is an old topic in ring theory. In, G. Tang et al: Unit Groups of Group Algebras of Some Small Groups. Czech. Math. J. 64 (2014), 149--157, the structure of the unit group of the group ring of the non abelian group $G$ with order $21$ over any finite field of characteristic 3 was established. In this paper, we are going to generalize their result to any non abelian group $G=T_{3m}$, where $T_{3m} = \langle x,y\,|\,x^m=y^3=1,\,x^y=x^t\…
