Automorphism groups of nilpotent groups

We construct a full class of nilpotent groups of class 2 of an arbitrary infinite cardinality . Their centers, commutator subgroups and factors modulo the center will be the same and a homogeneous direct sum of a group of rank 1 or 2. Their automorphism groups will coincide and the factor group modulo the stabilizer could be an arbitrary group of size $\leqq$ .     

Automorphism groups of pictures

A picture is a simple graph together with an edge-coloring, such that each vertex is incident with exactly one edge of each color. An automorphism of a picture is a graph automorphism that preserves the colors of the edges. We show that every group is isomorphic to the full automorphism group of a picture, and prove that a group is isomorphic to a vertex-transitive subgroup of the automorphism group of a picture if and only if it can be generated by involutions.     

Automorphism groups of fields

We consider pairs (K,G) of an infinite field K or a formally real field K and a group G and want to find extension fields F of K with automorphism group G. If K is formally real then we also want F to be formally real and G must be right orderable. Besides showing the existence of the desired extension fields F, we are mainly interested in the question about the smallest possible size of such fields. From some combinatorial tools, like Shelah’s Black Box, we inherit jumps in cardinalities of K and F respectively. For this reason we apply different methods in constructing fields F: We use a recent theorem on realizations of group rings as endomorphism rings in the category of free modules with distinguished submodules. Fortunately this theorem remains valid without cardinal jumps. In our main result (Theorem 1) we will show that for a large class of fields the desired result holds for extension fields of equal cardinality. This article was processed by the author using the LAT_EX style filecljour1 from Springer-Verlag     

Automorphism groups of polycyclic-by-finite groups and arithmetic groups

We show that the outer automorphism group of a polycyclic-by-finite group is an arithmetic group. This result follows from a detailed structural analysis of the automorphism groups of such groups. We use an extended version of the theory of the algebraic hull functor initiated by Mostow. We thus make applicable refined methods from the theory of algebraic and arithmetic groups. We also construct examples of polycyclic-by-finite groups which have an automorphism group which does not contain an arithmetic group of finite index. Finally we discuss applications of our results to the groups of homotopy self-equivalences of K(Γ,1)-spaces and obtain an extension of arithmeticity results of Sullivan in rational homotopy theory.     

Automorphism groups of nilpotent groups and spaces

A pair of finitely generated, torsion-free nilpotent groups G₁,G₂ is constructed with the properties that G₁ and G₂ are p-isomorphic for all primes p, yet Aut(G₁) and Aut(G₂) are not isomorphic. The example constructed is compared to an analogous example in the homotopy category of simply connected, finite CW-complexes.     

Automorphism groups of free metabelian nilpotent groups

Published in Algebra i Logika, Vol. 29, No. 6, pp. 746–751, November–December, 1990.     

Automorphism groups of Gabidulin-like codes

We compute the Clifford index of all curves on K3 surfaces with Picard group isomorphic to U(m).     

Automorphism groups of decidable models

It is proved that there exists no relationship between isomorphism types of the ordinary and recursive automorphism groups of recursive models and the property of being decidable for these models. Moreover, we show that all isomorphism types of recursive automorphism groups can be realized in a single (up to isomorphism) decidable countably categorical model. Taking account of the action of a group on the universe of the model makes it possible to distinguish between the classes of groups for decidable and all the recursive models.Translated fromAlgebra i Logika, Vol. 34, No. 4, pp. 437–447, July-August, 1995.     

Automorphism groups of algebraic lattices

We classify those algebraic lattices whose group of automorphisms is transitive on the set of elements of the lattice except the smallest and the greatest. We describe their automorphism groups in terms of generalized wreath powers.Presented by Bjarni Jonsson.     

Automorphism groups of finite posets

For any finite group G, we construct a finite poset (or equivalently, a finite T₀-space) X, whose group of automorphisms is isomorphic to G. If the order of the group is n and it has r generators, X has n(r+2) points. This construction improves previous results by G. Birkhoff and M.C. Thornton. The relationship between automorphisms and homotopy types is also analyzed.     

Automorphism groups of finite groupoids

Given a finite set M of size n and a subgroup G of Sym(M), G is pertinent iff it is the automorphism group of some groupoid ??M; *??. We examine when subgroups of Sym(M) are and are not pertinent. For instance, A _n , the alternating group on M, is not pertinent for n > 4. We close by indicating a natural extension of our ideas, which relates to a question of M. Gould.