Minimal orbit sizes in nilpotent group actions

Bera [Line graph characterization of power graphs of finite nilpotent groups, Comm. Algebra 50(11) (2022) 4652–4668] characterized finite nilpotent groups whose power graphs and proper power graphs are line graphs. In this paper, we extend the results of above-mentioned paper to arbitrary finite groups. Also, we correct the corresponding result of the proper power graphs of dihedral groups. Moreover, we classify all the finite groups whose enhanced power graphs are line graphs. We classify all the finite nilpotent groups (except non-abelian [Formula: see text]-groups) whose proper enhanced power graphs are line graphs of some graphs. Finally, we determine all the finite groups whose (proper) power graphs and (proper) enhanced power graphs are the complement of line graphs, respectively.

Recently, the concept of (normal) bent partitions, which are partitions of elementary abelian groups having similar properties to spreads, has been introduced by Anbar and Meidl. A large number of bent partitions, so-called generalized semifield spreads, can be obtained from semifields with certain properties. A strongly related concept, namely Latin square partial difference set packings (LP-packings) in finite abelian groups, has also been introduced recently by Jedwab and Li. The examples for LP-packings in an elementary abelian group are obtained from spreads. LP-packings yield bent partitions (not only for elementary abelian groups). In this paper, we first point out that conversely, generalized semifield spreads yield LP-packings. As a result, there is a huge amount of LP-packings in elementary abelian groups, other than spreads. With some examples from ternary bent functions, we then show that normal bent partitions and LP-packings are not the same concept. Finally, we extend the lifting procedure from spreads to LP-packings in nonelementary abelian groups to a lifting procedure from some generalized spreads to LP-packings in nonelementary abelian groups and in larger elementary abelian groups. This potentially yields bent partitions other than generalized semifield spreads.

P. Hall's classical equality for the number of conjugacy classes‎ ‎in $p$-groups yields $k(G) ge (3/2) log_2 |G|$ when $G$ is nilpotent‎. ‎Using only Hall's theorem‎, ‎this is the best one can do when $|G| = 2^n$‎. ‎Using a result of G.J‎. ‎Sherman‎, ‎we improve the constant $3/2$ to $5/3$‎, ‎which is best possible across all‎ ‎nilpotent groups and to $15/8$ when $G$ is nilpotent and $|G| ne 8,16$‎. ‎These results are then used to prove that $k(G) > log_3(|G|)$ when $G/N$ is nilpotent‎, ‎under ‎‎‎‎natural conditions on $N trianglelefteq G$‎. ‎Also‎, ‎when $G'$ is nilpotent of class $c$‎, ‎we prove that $k(G) ge (log |G|)^t$ when $|G|$ is large enough‎, ‎depending only on $(c,t)$‎.

In this article, it is shown that the normalizer property holds for the following two kinds of finite nilpotent-by-nilpotent groups: (1) G = NwrH is the standard wreath product of N by H, where N is a finite nilpotent group and H is a finite abelian 2-group; (2) G is a finite group having a normal nilpotent subgroup N such that the integral group ring ℤ(G/N) has only trivial units. Our results generalize a result of Yuanlin Li and extend some ones obtained by Juriaans, Miranda, and Robério.

The Amit conjecture about word maps on finite nilpotent groups has been shown to hold for certain classes of groups. The generalised Amit conjecture says that the probability of an element occurring in the image of a word map on a finite nilpotent group G is either 0, or at least 1/|G|. Noting the work of Ashurst, we name the generalised Amit conjecture the Amit–Ashurst conjecture and show that the Amit–Ashurst conjecture holds for finite p-groups with a cyclic maximal subgroup.

A power automorphism θ of a group G is said to be pre-fixed-point-free if CG(θ) is an elementary abelian 2-group. G is called an E-group if G has a pre-fixed-point-free power automorphism. In this paper, finite E-groups, together with all their pre-fixed-point-free power automorphisms, are completely determined. Moreover, a characteristic of finite abelian groups is given, which explains some known facts concerning power automorphisms.

Let G be a finite group, written multiplicatively. Define \({\mathsf{E}(G)}\) to be the minimal integer t such that every sequence of t elements (repetition allowed) in G contains a subsequence with length \({|G|}\) and with product one (in some order). Let p be the smallest prime divisor of \({|G|}\). In this paper we prove that if G is a noncyclic nilpotent group then \({\mathsf{E}(G) \le |G|+\frac{|G|}{p}+p-2}\), which confirms partially a conjecture by Gao and Li. We also determine the exact value of \({\mathsf{E}(G)}\) for \({G=C_{p}\ltimes C_{pn}}\) when p is a prime, which confirms partially another conjecture by Zhuang and Gao.

On the Number of Generators and Composition Length of Finite Linear Groups

For a group 𝐺, the enhanced power graph of 𝐺 is a graph with vertex set 𝐺 in which two distinct vertices x , y x,y are adjacent if and only if there exists an element 𝑤 in 𝐺 such that both 𝑥 and 𝑦 are powers of 𝑤. The proper enhanced power graph is the induced subgraph of the enhanced power graph on the set G ∖ S G\setminus S , where 𝑆 is the set of dominating vertices of the enhanced power graph. In this paper, we at first classify all nilpotent groups 𝐺 such that the proper enhanced power graphs are connected and calculate their diameter. We also explicitly calculate the domination number of the proper enhanced power graphs of finite nilpotent groups. Finally, we determine the multiplicity of the Laplacian spectral radius of the enhanced power graphs of nilpotent groups.

The enhanced power graph [Formula: see text] of a group [Formula: see text] is the graph with vertex set [Formula: see text] such that two vertices [Formula: see text] and [Formula: see text] are adjacent if they are contained in the same cyclic subgroup. We prove that finite groups with isomorphic enhanced power graphs have isomorphic directed power graphs. We show that any isomorphism between undirected power graph of finite groups is an isomorphism between enhanced power graphs of these groups, and we find all finite groups [Formula: see text] for which [Formula: see text] is abelian, all finite groups [Formula: see text] with [Formula: see text] being prime power, and all finite groups [Formula: see text] with [Formula: see text] being square-free. Also, we describe enhanced power graphs of finite abelian groups. Finally, we give a characterization of finite nilpotent groups whose enhanced power graphs are perfect, and we present a sufficient condition for a finite group to have weakly perfect enhanced power graph.

For $2 \leqq c \leqq \infty $, the c-linear complexity $L_c (A)$ of a complex matrix A is defined as the minimal number of additions, subtractions, and multiplications by complex constants of absolute value $ \leqq c$, sufficient to evaluate A at a generic input vector. It is shown that if A is a Fourier transform on the finite group G, then $| L_\infty (A) - L_\infty (A^{ - 1} ) | \leqq | G |$. $L_c (G): = \min \{ L_c (A)|A{\text{ a Fourier transform for }}G\} $ is called the c-linear complexity of the finite group G. It is proved that $L_2 (G) > \frac{1}{4}| G |\log | G |$ for any finite group G, and two infinite classes of non-abelian groups G with $L_2 (G) \leqq 0.6| G |\log | G |$ and $L_2 (G) \leqq 0.8| G |\log | G |$, respectively, are presented. Thus there are non-abelian groups with even faster Fourier transforms than elementary abelian 2-groups (for which $L_2 (G) \leqq | G |\log | G |$)!

We show that, for a positive integer r, every minimal 1-saturating set in ${PG}(r-1,2)$ of size at least $\frac{11}{36}\,2^r+3$ either is a complete cap or can be obtained from a complete cap S by fixing some $s\in S$ and replacing every point $s'\in S\setminus\{s\}$ by the third point on the line through s and $s'$. Since, conversely, every set obtained in this way is a minimal 1-saturating set and the structure of large sum-free sets in an elementary abelian 2-group is known, this provides a complete description of large minimal 1-saturating sets. An algebraic restatement is as follows. Suppose that G is an elementary abelian 2-group and a subset $A\subseteq G\setminus\{0\}$ satisfies $A\cup2A=G$ and is minimal subject to this condition. If $|A|\ge\frac{11}{36}\,|G|+3$, then either A is a maximal sum-free set or there are a maximal sum-free set $S\subseteq G$ and an element $s\in S$ such that $A=\{s\}\cup\bigl(s+(S\setminus\{s\})\bigr)$. Our approach is based on characterizing those large sets A in elementary abelian 2-groups such that, for every proper subset B of A, the sumset $2B$ is a proper subset of $2A$.

Thin bases for finite nilpotent groups

Suppose that $A,B$ are non-empty subsets of the finite nilpotent group $G$. If $A\not=B$, then the cardinality of the restricted sumset $$A\mathbin\dotplus B=\{a+b:a\in A,\, b\in B,\, a\neq b\} $$ is at least $$\min\{p(G),|A|+|B|-2\},$$ where $p(G)$

The work in this article was motivated by a question about Fibonacci sequences in groups. Let a, b be arbitrary elements of a group G. We define a Fibonacci sequence in G as for the integers. Let x0 = a, x1 = b and xn+1 = xn−1xn. In [3], Wall investigated the length of the fundamental period of the Fibonacci sequence in a finite cyclic group. Aydin and Smith [1] looked more generally at finite nilpotent groups. The study quickly reduces to finite p-groups. Denote by k(G), the length of the fundamental period of the Fibonacci sequence in G. Aydin and Smith proved the following theorem that generalises a result that Wall obtained in the cyclic case.