On Endo-trivial Modules for p-Solvable Groups

Endo-trivial modules for finite groups with dihedral Sylow 2-subgroup

Let $k$ be an algebraically closed field of characteristic $p>0$ and $G$ a finite group. We provide a description of the torsion subgroup $TT(G)$ of the finitely generated abelian group $T(G)$ of endo-trivial $kG$-modules when $p=2$ and $G$ has a dihedral Sylow $2$-subgroup $P$. We prove that, in the case $|P|\geq 8$, $TT(G)\cong X(G)$ the group of one-dimensional $kG$-modules, except possibly when $G/O_{2'}(G)\cong \mathfrak{A}_6$, the alternating group of degree $6$; in which case $G$ may have $9$-dimensional simple torsion endo-trivial modules. We also prove a similar result in the case $|P…

Gluing Borel-Smith functions and the group of endo-trivial modules

The aim of this paper is to describe the group of endo-trivial modules for a $p$-group $P$, in terms of the obstruction group for the gluing problem of Borel-Smith functions.

Endo-trivial modules for finite groups with Klein-four Sylow 2-subgroups

We study the finitely generated abelian group $T(G)$ of endo-trivial $kG$-modules where $kG$ is the group algebra of a finite group $G$ over a field of characteristic $p>0$. When the representation type of the group algebra is not wild, the group structure of $T(G)$ is known for the cases where a Sylow $p$-subgroup $P$ of $G$ is cyclic, semi-dihedral and generalized quaternion. We investigate $T(G)$, and more accurately, its torsion subgroup $TT(G)$ for the case where $P$ is a Klein-four group. More precisely, we give a necessary and sufficient condition in terms of the centralizers of involut…

Universal deformation rings, endo-trivial modules, and semidihedral and generalized quaternion 2-groups

Let $k$ be a field of characteristic $p>0$, and let $W$ be a complete discrete valuation ring of characteristic $0$ that has $k$ as its residue field. Suppose $G$ is a finite group and $G^{\mathrm{ab},p}$ is its maximal abelian $p$-quotient group. We prove that every endo-trivial $kG$-module $V$ has a universal deformation ring that is isomorphic to the group ring $WG^{\mathrm{ab},p}$. In particular, this gives a positive answer to a question raised by Bleher and Chinburg for all endo-trivial modules. Moreover, we show that the universal deformation of $V$ over $WG^{\mathrm{ab},p}$ is uniquely…

The classification of torsion endo-trivial modules

This paper is a major step in the classification of endotrivial modules over p-groups. Let G be a finite p-group and k be a field of characteristic p. A kG-module M is an endo-trivial module if {\End_k(M)\cong k\oplus F} as kG-modules, where F is a free module. The classification of endo-trivial modules is the crucial step for understanding the more general class of endo-permutation modules. The endo-permutation modules play an important role in module theory, in particular as source modules, and in block theory where they appear in the description of source algebras. Endo-trivial modules are …

Random walks on dyadic-valued solvable matrix groups

This paper is concerned with random walks on a family of dyadic-valued solvable matrix groups. A description of the Poisson boundary of these groups for probability measures of finite first moment and non-zero displacements (or drifts) is given. When non-trivial, the boundary may be identified with a space of matrices with real and 2-adic entries, depending on the values in a displacement matrix associated with the random walk. Conditions for boundary triviality are also discussed.

On the intersection of solvable Hall subgroups in finite simple exceptional groups of Lie type

Assume that a finite almost simple group with simple socle isomorphic to an exceptional group of Lie type possesses a solvable Hall subgroup. Then there exist four conjugates of the subgroup such that their intersection is trivial.

Schwartz functions, tempered distributions, and Kernel Theorem on solvable Lie groups

Let G be a solvable Lie group endowed with right Haar measure. We define and study a dense Frechet *-subalgebra S of L1(G), consisting of smooth functions rapidly-decreasing at infinity on G. When G is nilpotent, we recover the classical Schwartz algebra introduced by R. Howe and other authors. We develop a distribution theory for S, and we generalize the classical Kernel Theorem of L. Schwartz to our setting.

关于可解的Baumslag-Solitar群中的固定点和稳定化子

On fixed points and stabilizers in solvable Baumslag--Solitar groups

本文研究了可解Baumslag-Solitar群中的固定点和稳定化子，证明了自同构和满射下的固定点子群及稳定化子的结构特性。

可解置换群中的集合稳定子

Set-stabilizers in solvable permutation groups

本文证明了有限可解置换群中，模去可能平凡的正则初等交换3-子群后，必存在某个集合稳定子为2-群。

紧群的可扩张自同态

Extensible endomorphisms of compact groups

本文刻画了紧连通群上可扩张到所有紧超群的自同态，证明其仅为平凡自同态和内自同构，并发现紧连通阿贝尔群情形还额外包含负恒等自同态。

Singularity of the varieties of representations of lattices in solvable Lie groups

For a lattice $Γ$ of a simply connected solvable Lie group $G$, we describe the analytic germ in the variety of representations of $Γ$ at the trivial representation as an analytic germ which is linearly embedded in the analytic germ associated with the nilpotent Lie algebra determined by $G$. By this description, under certain assumption, we study the singularity of the analytic germ in the variety of representations of $Γ$ at the trivial representation by using the Kuranishi space construction. By a similar technique, we also study deformations of holomorphic structures of trivial vector bund…

Intersection of Solvable Hall subgroups in finite groups

In this paper we show that if S is a simple classical group, a group G is contained in inner-diagonal automorphisms of S and contains S, and H is a solvable Hall subgroup of G, then there exists five conjugates of H, whose intersection is trivial.

Endotrivial representations of finite groups and equivariant line bundles on the Brown complex

We relate endotrivial representations of a finite group in characteristic p to equivariant line bundles on the simplicial complex of non-trivial p-subgroups, by means of weak homomorphisms.

On the base size of a transitive group with solvable point stabilizer

We prove that the base size of a transitive group $G$ with solvable point stabilizer and with trivial solvable radical is not greater than $k$ provided the same statement holds for the group of $G$-induced automorphisms of each nonabelian composition factor of $G$.

Blocks of defect of p-solvable groups

Let $p$ be a prime such that $p \geq 5$. Let $G$ be a finite $p$-solvable group and let $p^a$ be the largest power of $p$ dividing $χ(1)$ for an irreducible character $χ$ of $G$, we show that $|G:F(G)|_p \leq p^{5.5a}$. Let $G$ be a finite $p$-solvable group with trivial maximal normal solvable subgroup and we denote $|G|_p=p^n$, then $G$ contains a block of defect less than or equal to $\lfloor \frac {2n} {3} \rfloor$.

非可解群的非线性特征度数具有相同不同素因子数

Non-solvable groups whose non-linear character degrees have the same number of different prime divisors

本文研究非可解群的非线性特征度数具有相同不同素因子数的性质，证明此类群在可解因子作用下仅限于特定几类群，并验证Huppert的ρ-σ猜想。

Obstruction to a Higman embedding theorem for residually finite groups with solvable word problem

We prove that, for a finitely generated residually finite group, having solvable word problem is not a sufficient condition to be a subgroup of a finitely presented residually finite group. The obstruction is given by a residually finite group with solvable word problem for which there is no effective method that allows, given some non-identity element, to find a morphism onto a finite group in which this element has a non-trivial image. We also prove that the depth function of this group grows faster than any recursive function.

Three-dimensional loops as sections in a four-dimensional solvable Lie group

We classify all three-dimensional connected topological loops such that the group topologically generated by their left translations is the four-dimensional connected Lie group $G$ which has trivial center and precisely two one-dimensional normal subgroups. We show that $G$ is not the multiplication group of connected topological proper loops.

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。

$\frac{3}{2}$-传递置换群的置换模的自同态环

The endomorphism rings of permutation modules of $\frac{3}{2}$-transitive permutation groups

本文针对 $\frac{3}{2}$-传递置换群的六类分类结果，通过逐类分析证明了其自然置换模的自同态环均为对称代数。

Classifying Solvable Primitive Permutation Groups of Low Rank

Suppose that $G$ is a finite, transitive, solvable permutation group acting on a set $S$ with $n$ elements. Let $G_0$ be the stabilizer of a point $α\in Ω$. Define the rank of a permutation group, denoted $r(G),$ as the number of distinct orbits of $G_0$ in $S$ (including the trivial orbit $\{α\}$). Huppert \cite{Huppert} and Foulser \cite{Foulser} classified all finite, solvable, permutation groups of rank two and three respectively, and Foulser restricted the rank four groups to a small list of possibilities. This paper completes the classification of all groups of rank less than $5$ by expl…

Intersection of conjugate solvable subgroups in finite classical groups

We consider the following problem stated by Vdovin (2010) in the "Kourovka notebook" (Problem 17.41): Let $H$ be a solvable subgroup of a finite group $G$ that has no nontrivial solvable normal subgroups. Do there always exist five conjugates of $H$ whose intersection is trivial? This problem is closely related to a conjecture by Babai, Goodman and Pyber (1997) about an upper bound for the index of a normal solvable subgroup in a finite group. In particular, a positive answer to Vdovin's problem yields that if $G$ has a solvable subgroup of index $n$, then it has a solvable normal subgroup of …

分类秩为5和6的本原可解置换群

Classifying Primitive Solvable Permutation Groups of Rank 5 and 6

本文完整分类了秩为5和6的有限本原可解置换群，延续了先前对秩4及以下群的分类工作，给出了所有此类群的结构描述。

Inertial endomorphisms of an abelian group

We describe inertial endomorphisms of an abelian group $A$, that is endomorphisms $φ$ with the property $|(φ(X)+X)/X|<\infty$ for each $X\le A$. They form a ring containing multiplications, the so-called finitary endomorphisms and non-trivial instances. We show that inertial invertible endomorphisms form a group, provided $A$ has finite torsion-free rank. In any case, the group $IAut(A)$ they generate is commutative modulo the group $FAut(A)$ of finitary automorphisms, which is known to be locally finite. We deduce that $IAut(A)$ is locally-(center-by-finite). Also we consider the lattice dual…

A geometric classification of some solvable groups of homeomorphisms

We investigate subgroups of the group PLo(I) of piecewise-linear, orientation-preserving homeomorphisms of the unit interval with finitely many breaks in slope, under the operation of composition, and also subgroups of the generalized Thompson groups F_n. We find geometric criteria determining the derived length of any such group, and use this criteria to produce a geometric classification of the solvable and non-solvable subgroups of PLo(I) and of the F_n. We also show that any standard restricted wreath product C wr T (of non-trivial groups) that embeds in PLo(I) or F_n must have T isomorphi…

非可解群中的元素阶与特征标余次数

Element orders and codegrees of characters in non-solvable groups

该研究在有限群特征标余次数的Qian猜想已有可解群、殆单群验证基础上，证明猜想对Fitting子群平凡的有限群成立，且完整猜想分析可归约为具可解基座的群。

Gluing endo-permutation modules

In this paper, I show that if $p$ is an odd prime, and if $P$ is a finite $p$-group, then there exists an exact sequence of abelian groups $$0\to T(P)\to D(P)\to\lproj{P}\to H^1\big(\apdeux(P),\Z\big)^{(P)},$$ where $D(P)$ is the Dade group of $P$ and $T(P)$ is the subgroup of endo-trivial modules. Here $\lproj{P}$ is the group of sequences of compatible elements in the Dade groups $D\big(N_P(Q)/Q\big)$ for non trivial subgroups $Q$ of $P$. The poset $\apdeux(P)$ is the set of elementary abelian subgroups of rank at least 2 of $P$, ordered by inclusion. The group $H^1\big(\apdeux(P),\Z\big)^{(…

具有可解稳定子的有限线性群的基的大小

Base sizes for finite linear groups with solvable stabilisers

本文针对点稳定子可解、可解根基平凡的传递置换群的基大小猜想，证明了基柱同构于PSL_n(q)的殆单群情形下该猜想的强形式，其余典型群将在后续论文处理。

Subgroup posets, Bredon cohomology and equivariant Euler characteristics

For a discrete group $Γ$ satisfying some finiteness conditions we give a Bredon projective resolution of the trivial module in terms of projective covers of the chain complex associated to certain posets of subgroups. We use this to give new results on dimensions of $Eγ$ and to reprove that for virtually solvable groups, $\underline{\cd}Γ=\vcdΓ$. We also deduce a formula to compute the Euler class of $Eγ$ for $Γ$ virtually solvable of type $\FP_\infty$ and use it to compute orbifold Euler characteristics.

Strongly Embedded Subgroups of Groups of Odd Type

In this paper we prove that any strongly embedded subgroup of a K*-group G of finite Morley rank and odd type that does not interpret any bad field is solvable if its Pruefer 2-rank is at least 2. If the normal 2-rank of G is at least 3 this has two important consequences: If G contains a non-solvable centraliser of an involution, then G does not contain any proper 2-generated core and centralisers of involutions have trivial cores.