On the inheriting of the property $C_π$ by some normal subgroups

The normal subgroup structure of ZM-groups

The main goal of this note is to determine and to count the normal subgroups of a ZM-group. We also indicate some necessary and sufficient conditions such that the normal subgroups of a ZM-group form a chain.

Intersecting free subgroups in free amalgamated products of two groups with normal finite amalgamated subgroup

We partly generalize the estimate for the rank of intersection of subgroups in free products of groups, proved earlier by S.V.Ivanov and W.Dicks, to the case of free amalgamated products of groups with normal finite amalgamated subgroup. We also prove that the obtained estimate is sharp and cannot be further improved when the amalgamated product contains an involution.

Finite groups with Frobenius normalizer condition for non-normal primary subgroups

A finite group $P$ is said to be \emph{primary} if $|P|=p^{a}$ for some prime $p$. We say a primary subgroup $P$ of a finite group $G$ satisfies the \emph{Frobenius normalizer condition} in $G$ if $N_{G}(P)/C_{G}(P)$ is a $p$-group provided $P$ is $p$-group. In this paper, we determine the structure of a finite group $G$ in which every non-subnormal primary subgroup satisfies the Frobenius normalized condition. In particular, we prove that if every non-normal primary subgroup of $G$ satisfies the Frobenius condition, then $G/F(G)$ is cyclic and every maximal non-normal nilpotent subgroup $U$ o…

On Normal Subgroups of Coxeter Groups Generated by Standard Parabolic Subgroups

We discuss one construction of nonstandard subgroups in the category of Coxeter groups. Two formulae for the growth series of such a subgroups are given. As an application we construct a flag simple convex polytope, whose f-polynomial has non-real roots.

On normal subgroupoids

In this paper we present some algebraic properties of subgroupoids and normal subgroupoids. We define the normalizer of a wide subgroupoid $\mathcal{H}$ and show that, as in the case of groups, the normalizer is the greatest wide subgroupoid of the groupoid $\mathcal{G}$ in which $\mathcal{H}$ is normal. Furthermore, we give the definition of center and commutator and prove that both are normal subgroupoids, the first one of the union of all the isotropy groups of $\mathcal{G}$ and the second one of $\mathcal{G}$. Finally, we introduce the concept of inner isomorphism of $\mathcal{G}$ and show…

具有某些特定极大不变子群为幂零或所有非幂零极大不变子群均为正规的有限群

Finite groups with some particular maximal invariant subgroups being nilpotent or all non-nilpotent maximal invariant subgroups being normal

本文分类了在互素自同构群作用下、含某不变 Sylow 子群正规化子的极大不变子群均为幂零的有限群，并证明该条件等价于所有非幂零极大不变子群均正规。

Automorphisms fixing every normal subgroup of a nilpotent-by-abelian group

Among other things, we prove that the group of automorphisms fixing every normal subgroup of a nilpotent-by-abelian group is nilpotent-by-metabelian. In particular, the group of automorphisms fixing every normal subgroup of a metabelian group is soluble of derived length at most 3. An example shows that this bound cannot be improved.

Three amalgams with remarkable normal subgroup structures

We construct three groups $Λ_1$, $Λ_2$, $Λ_3$, which can all be decomposed as amalgamated products $F_9 \ast_{F_{81}} F_{9}$ and have very few normal subgroups of finite or infinite index. Concretely, $Λ_1$ is a simple group, $Λ_2$ is not simple but has no non-trivial normal subgroup of infinite index, and $Λ_3$ is not simple but has no proper subgroup of finite index.

New normal subgroups for the group representation of the Cayley tree

In this paper we give full description of normal subgroups of index eight and ten for the group.

Groups with finiteness conditions on the lower central series of non-normal subgroups

It is known that any locally graded group with finitely many derived subgroups of non-normal subgroups is finite-by-abelian. This result is generalized here, by proving that in a locally graded group $G$ the subgroup $γ_{k}(G)$ is finite if the set $\{γ_{k}(H)\;|\;H\ntriangleleft G\}$ is finite. Moreover, locally graded groups with finitely many $k$th terms of lower central series of infinite non-normal subgroups are also completely described.

On open normal subgroups of parahorics

Let $F$ be a local complete field with discrete valuation, and let $G$ be a quasi-split group over $F$ which splits over some unramified extension of $F$. Let $P$ be a parahoric subgroup of the group $G(F)$ of $F$-points of $G$; t he open normal pro-nilpotent subgroups of $P$ can be classified using the standa rd normal filtration subgroups of Prasad and Raghanathan. More precisely, we sho w that if $G$ is quasi-simple and satisfies some additional conditions, $H$ is, modulo a subgroup of some maximal torus of $G$, either one of these filtration s ubgroups or the product of one of them by a st…

On the Absence of a Normal Nonabelian Sylow Subgroup

Let $G$ be a finite solvable group. We show that $G$ does not have a normal nonabelian Sylow $p$-subgroup when its prime character degree graph $Δ(G)$ satisfies a technical hypothesis.

Products of partial normal subgroups

We show that the product of two partial normal subgroups of a locality (in the sense of Chermak) is again a partial normal subgroup. This generalizes a theorem of Chermak and fits into the context of building a local theory of localities.

Groups in which each subgroup is commensurable with a normal subgroup

A group G is a cn-group if for each subgroup H of G there exists a normal subgroup N of G such that the index of both H and N in HN is finite. The class of cn-groups contains properly the classes of core- finite groups and that of groups in which each subgroup has finite index in a normal subgroup. In the present paper it is shown that a cn-group whose periodic images are locally finite is finite-by-abelian-by-finite. Such groups are then described into some details by considering automorphisms of abelian groups. Finally, it is shown that if G is a locally graded group with the property that t…

Locally normal subgroups and ends of locally compact Kac-Moody groups

A locally normal subgroup in a topological group is a subgroup whose normaliser is open. In this paper, we provide a detailed description of the large-scale structure of closed locally normal subgroups of complete Kac-Moody groups over finite fields. Combining that description with the main result from arXiv:2111.07066, we show that under mild assumptions, if the Kac-Moody group is one-ended (a property that is easily determined from the generalised Cartan matrix), then it is locally indecomposable, which means that no open subgroup decomposes as a nontrivial direct product.

关于正规子群不变横截面的注记

A note on invariant transversals for normal subgroups

本文研究了有限群中阿贝尔正规子群的不变横截面存在性，并给出了相关猜想的反例。

On groups whose subnormal abelian subgroups are normal

In the current paper we study the groups, whose subnormal abelian subgroups are normal. We obtained a quite detailed description of such hyperabelian groups with a periodic Baer radical. The description of hyperabelian Lie algebras, whose abelian subideals are ideals, is also obtained.

具有幂零正规补子群的有限可解群

Finite solvable groups with a nilpotent normal complement subgroup

本文研究有限可解群中非正规无核子群的结构，证明在特定正规化子条件下，该子群存在幂零正规补，且相关构造形成Frobenius群。

A note on the normal subgroup lattice of ultraproducts of finite quasisimple groups

In [A. Stolz and A. Thom, On the lattice of normal subgroups in ultraproducts of compact simple groups, PLMS 108(1), 2014] it was stated that the lattice of normal subgroups of an ultraproduct of finite simple groups is always linearly ordered. This is false in this form in most cases for classical groups of Lie type. We correct the statement and point out a version of 'relative' bounded generation results for classical quasisimple groups and its implications on the structure of the lattice of normal subgroups of an ultraproduct of quasisimple groups.

Automorphisms of semidirect products fixing the non-normal subgroup

In this paper, we describe the automorphism group of semidirect product of two groups that fixes the non-normal subgroup of it. We have computed these automorphisms for the non-abelian metacyclic $p$-group and non-abelian $p$-groups $(p\ge 5)$ of order $p^{4}$, where $p$ is a prime.

Finite groups determined by an inequality of the orders of their normal subgroups

In this article we introduce and study a class of finite groups for which the orders of normal subgroups satisfy a certain inequality. It is closely connected to some well-known arithmetic classes of natural numbers.

从特征标表确定的正规子群的某些性质

Some Properties of normal subgroups determined from character tables

本文分析了可从G特征标表确定的正规子群结构性质，扩展了Thompson定理和Taketa定理，并引入了幂零类受不可约特征标度数量界定的新类nMI群。

Coxeter群及其自同构群的窄正规子群

Narrow normal subgroups of Coxeter groups and of automorphism groups of Coxeter groups

本文研究Coxeter群及其自同构群中的正规子群，刻画了其中有限子群与不含非阿贝尔自由群的窄子群的结构。

A sharply 2-transitive group without a non-trivial abelian normal subgroup

We show that any group $G$ is contained in some sharply 2-transitive group $\mathcal{G}$ without a non-trivial abelian normal subgroup. This answers a long-standing open question. The involutions in the groups $\mathcal{G}$ that we construct have no fixed points.

Normal subgroups in the group of column-finite infinite matrices

The classical result, due to Jordan, Burnside, Dickson, says that every normal subgroup of $GL(n, K)$ ($K$ - a field, $n \geq 3$) which is not contained in the center, contains $SL(n, K)$. A. Rosenberg gave description of normal subgroups of $GL(V)$, where $V$ is a vector space of any infinite cardinality dimension over a division ring. However, when he considers subgroups of the direct product of the center and the group of linear transformations $g$ such that $g-id_V$ has finite dimensional range the proof is not complete. We fill this gap for countably dimensional $V$ giving description of …

Virtually free finite-normal-subgroup-free groups are strongly verbally closed

Any virtually free group $H$ containing no non-trivial finite normal subgroup (e.g., the infinite dihedral group) is a retract of any finitely generated group containing $H$ as a verbally closed subgroup.

On a finite group having a normal series whose factors have bicyclic Sylow subgroups

We consider the structure of a finite groups having a normal series whose factors have bicyclic Sylow subgroups. In particular, we investigated groups of odd order and $A_4$-free groups with this property. Exact estimations of the derived length and nilpotent length of such groups are obtained.

A Normal Subgroup Theorem for Commensurators of Lattices

We establish a general normal subgroup theorem for commensurators of lattices in locally compact groups. While the statement is completely elementary, its proof, which rests on the original strategy of Margulis in the case of higher rank lattices, relies heavily on analytic tools pertaining to amenability and Kazhdan's property (T). It is a counterpart to the normal subgroup theorem for irreducible lattices of Bader and the second named author, and may also be used to sharpen that result when one of the ambient factors is totally disconnected.

A formula for the normal subgroup growth of Baumslag-Solitar groups

We give an exact formula for the number of normal subgroups of each finite index in the Baumslag-Solitar group BS(p,q) when p and q are coprime. Unlike the formula for all finite index subgroups, this one distinguishes different Baumslag-Solitar groups and is not multiplicative. This allows us to give an example of a finitely generated profinite group which is not virtually pronilpotent but whose zeta function has an Euler product.

正规子群超循环嵌入的新刻画

New characterizations of a normal subgroup to be hypercyclically embedded

本文研究群的正规子群超循环嵌入条件，基于主因子循环性给出若干新刻画，推广并统一了相关近期结果。

Groups in which every non-nilpotent subgroup is self-normalizing

We study the class of groups having the property that every non-nilpotent subgroup is equal to its normalizer. These groups are either soluble or perfect. We completely describe the structure of soluble groups and finite perfect groups with the above property. Furthermore, we give some structural information in the infinite perfect case.

Normal Subgroups of Powerful $p$ -groups

In this note we show that if $p$ is an odd prime and $G$ is a powerful $p$-group with $N\leq G^{p}$ and $N$ normal in $G$, then $N$ is powerfully nilpotent. An analogous result is proved for $p=2$ when $N\leq G^{4}$.

Normal subgroup growth in free class-2-nilpotent groups

Let $F_{2,d}$ denote the free class-2-nilpotent group on $d$ generators. We compute the normal zeta functions $ζ^\triangleleft_{F_{2,d}}(s)$, prove that they satisfy local functional equations and determine their abscissae of convergence and pole orders.

Groups in which every non-abelian subgroup is self-normalized

We study groups having the property that every non-abelian subgroup is equal to its normalizer. This class of groups is closely related to an open problem posed by Berkovich. We give a full classification of finite groups having the above property. We also describe all infinite soluble groups in this class.

Some Characterizations of a Normal Subgroup of a Group

Let G be a group and H be a subgroup of G which is either finite or of finite index in G. In this note, we give some characterizations for normality of H in G. As a consequence we get a very short and elementary proof of the Main Theorem of [5], which avoids the use of the classification of finite simple groups

The class $\mathcal{MN}$ of groups in which all maximal subgroups are normal

We investigate the class $\mathcal{MN}$ of groups with the property that all maximal subgroups are normal. The class $\mathcal{MN}$ appeared in the framework of the study of potential counter-examples to the Andrews-Curtis conjecture. In this note we give various structural properties of groups in $\mathcal{MN}$ and present examples of groups in $\mathcal{MN}$ and not in $\mathcal{MN}$.

作用于$\ ilde A_2$-建筑上的群的正规子群定理

Normal Subgroup Theorem for groups acting on $\tilde A_2$-buildings

本文证明了作用于$\ ilde A_2$型建筑且具有有限稳定子和有限基本域的群，其任何非平凡正规子群都是有限指数的。

Locally normal subgroups of simple locally compact groups

We announce various results concerning the structure of compactly generated simple locally compact groups. We introduce a local invariant, called the structure lattice, which consists of commensurability classes of compact subgroups with open normaliser, and show that its properties reflect the global structure of the ambient group.

Normal subgroups of odd-order monomial $p^a q^b$ groups

A finite group $G$ is called monomial if every irreducible character of $G$ is induced from a linear character of some subgroup of $G$. One of the main questions regarding monomial groups is whether or not a normal subgroup $N$ of a monomial group $G$ is itself monomial. In the case that $G$ is a group of even order, it has been proved (Dade, van der Waall) that $N$ need not be monomial. Here we show that, if $G$ is a monomial group of order $p^aq^b$, where $p$ and $q$ are distinct odd primes, then any normal subgroup $N$ of $G$ is also monomial.

A note on groups with self-normalizing cyclic subgroups

In this article, we prove that if all non-trivial cyclic subgroups of a group $G$ are self normalizing and $G$ satisfies the implication $$ \ o(x)\neq o(y)\Rightarrow o(xy)\neq o(x), o(y), $$ for all non-trivial elements $x$ and $y$, then $G$ is a $p$-group or simple.

Normalizers and centralizers of $p$-subgroups in normal subsystems of fusion systems

Suppose $\mathcal{E}$ is a normal subsystem of a saturated fusion system $\mathcal{F}$ over $S$. If $X\leq S$ is fully $\mathcal{F}$-normalized, then Aschbacher defined a normal subsystem $N_{\mathcal{E}}(X)$ of $N_{\mathcal{F}}(X)$. In this short note we revisit and generalize this result using the theory of localities. Our more general approach leads in particular to a normal subsystem $C_{\mathcal{E}}(X)$ of $C_{\mathcal{F}}(X)$ for every $X\leq S$ which is fully $\mathcal{F}$-centralized.

The kernel of the adjoint representation of a p-adic Lie group need not have an abelian open normal subgroup

Let G be a p-adic Lie group and Ad be the adjoint representation of G on its Lie algebra. It was claimed in the literature that the kernel K of Ad always has an abelian open normal subgroup. We show by means of a counterexample that this assertion is false; it can even happen that K=G but G has no abelian subnormal subgroup except for the trivial group. The arguments are based on auxiliary results on subgroups of free products with central amalgamation.

Centralizers of normal subgroups and the $Z^*$-Theorem

Glauberman's $Z^*$-theorem and analogous statements for odd primes show that, for any prime $p$ and any finite group $G$ with Sylow $p$-subgroup $S$, the centre of $G/O_{p^\prime}(G)$ is determined by the fusion system $\mathcal{F}_S(G)$. Building on these results we show a statement that seems a priori more general: For any normal subgroup $H$ of $G$ with $O_{p^\prime}(H)=1$, the centralizer $C_S(H)$ is expressed in terms of the fusion system $\mathcal{F}_S(H)$ and its normal subsystem induced by $H$.

通过特征标次数刻画正规 Hall 子群，II

Characterizing normal Hall subgroups by character degrees, II

本文证明了有限单经典群中真非平凡 Hall 子群的特征标次数性质，从而结合已有约化，给出了任意有限群中 Hall 子群正规性的充要条件：其诱导表示的不可约成分次数均为 $\pi'$ 数。

Lifts of partial characters with respect to a chain of normal subgroups

In this paper, we consider lifts of $π$-partial characters with the property that the irreducible constituents of their restrictions to certain normal subgroups are also lifts. We will show that such a lift must be induced from what we call an inductive pair, and every character induced from an inductive pair is a such a lift. With this condition, we will get a lower bound on the number of such lifts.

具有一个共轭类是两个正规子群差的群

Groups with a conjugacy class that is the difference of two normal subgroups

研究有限群中存在两个正规子群差作为共轭类的结构，通过特征理论刻画并确定此类群的性质，进一步推广了Gagola的结果。

置换群关于非交换极小正规子群的商

Quotients of permutation groups by nonabelian minimal normal subgroups

本文证明了 Sym(n) 的子群关于非交换极小正规子群的商可嵌入更小次数的置换群，并在传递情况下给出了次数的上界 m \le 2n/5。

关于分裂扩张的正规子群

On the normal subgroups of a split extension

本文通过N和Q的正规子群描述半直积G=N⋊Q的正规子群，其中N和Q是互素的有限群，并给出循环Sylow子群的有限群的正规子群完全列表。

Finite groups in which every maximal subgroup is nilpotent or normal or has $p'$-order

Let $G$ be a finite group and $p$ a fixed prime divisor of $|G|$. Combining the nilpotence, the normality and the order of groups together, we prove that if every maximal subgroup of $G$ is nilpotent or normal or has $p'$-order, then (1) $G$ is solvable; (2) $G$ has a Sylow tower; (3) There exists at most one prime divisor $q$ of $|G|$ such that $G$ is neither $q$-nilpotent nor $q$-closed, where $q\neq p$.

共轭类图直径为三的正规子群

Normal subgroups whose conjugacy class graph has diameter three

本文研究了有限群 $G$ 的正规子群 $N$，确定了当包含在 $N$ 中的 $G$-共轭类相关联的图的直径达到最大值三时 $N$ 的结构。

Normal subgroups of SimpHAtic groups

A group is SimpHAtic if it acts geometrically on a simply connected simplicially hereditarily aspherical (SimpHAtic) complex. We show that finitely presented normal subgroups of the SimpHAtic groups are either: finite, or of finite index, or virtually free. This result applies, in particular, to normal subgroups of systolic groups. We prove similar strong restrictions on group extensions for other classes of asymptotically aspherical groups. The proof relies on studying homotopy types at infinity of groups in question. We also show that nonuniform lattices in SimpHAtic complexes (and in more g…

正规子群共轭类图中的三角形

Triangles in the graph of conjugacy classes of normal subgroups

研究有限群正规子群共轭类图无三角形或恰有一个三角形时的结构，给出了相应的刻画。

On Normal Subgroups of Product of Groups

The object of this paper is to find a necessary and sufficient condition for the groups $G_1, G_2, ..., G_n$ so that every normal subgroup of the product $\prod_{i=1}^{n} G_i$ is of the type $\prod_{i=1}^{n} N_i$ with $N_i \trianglelefteq G_i$, $i=1,2, ..., n$. As a consequence we obtain a well-known result due to R. Remak about centreless completely reducible groups having finitely many direct factors.

不可约反射群的正规反射子群格

The lattice of normal reflection subgroups of an irreducible reflection group

研究不可约反射群的正规反射子群格，通过考虑共轭作用轨道给出计算方法及生成元，将复反射群分类表示为最大反射群集合及正规子群，研究商群和共线群作用，还引入新技术。