scholarly journals Modular group actions on algebras and p-local Galois extensions for finite groups

2015 ◽  
Vol 442 ◽  
pp. 316-353 ◽  
Author(s):  
Peter Fleischmann ◽  
Chris Woodcock
Keyword(s):  
Finite Groups ◽  
Modular Group ◽  
Group Actions ◽  
Galois Extensions

scholarly journals PSL(2, q) as an image of the extended modular group with applications to group actions on surfaces

1987 ◽  
Vol 30 (1) ◽  
pp. 143-151 ◽  
Author(s):  
David Singerman
Keyword(s):  
Free Product ◽  
Cyclic Group ◽  
Modular Group ◽  
Prime Power ◽  
Group Actions ◽  
Index 2 ◽  
Image Position

The modular group PSL(2, ℤ), which is isomorphic to a free product of a cyclicgroupof order 2 and a cyclic group of order 3, has many important homomorphic images. Inparticular, Macbeath [7] showed that PSL(2, q) is an image of the modular group if q ≠ 9. (Here, as usual, q is a prime power.) The extended modular group PGL(2, ℤ) contains PSL{2, ℤ) with index 2. It has a presentationthe subgroup PSL(2, ℤ) being generated by UV and VW.

Polarization of Separating Invariants

2008 ◽  
Vol 60 (3) ◽  
pp. 556-571 ◽  
Author(s):  
Jan Draisma ◽  
Gregor Kemper ◽  
David Wehlau
Keyword(s):  
Finite Group ◽  
Finite Groups ◽  
Group Actions ◽  
Upper Bounds ◽  
Weyl’S Theorem ◽  
Finite Group Actions ◽  
Separating Invariants ◽  
The Difference ◽  
Special Case

AbstractWe prove a characteristic free version of Weyl’s theorem on polarization. Our result is an exact analogue ofWeyl’s theorem, the difference being that our statement is about separating invariants rather than generating invariants. For the special case of finite group actions we introduce the concept of cheap polarization, and show that it is enough to take cheap polarizations of invariants of just one copy of a representation to obtain separating vector invariants for any number of copies. This leads to upper bounds on the number and degrees of separating vector invariants of finite groups.

Coprime Group Actions Fixing All Nonlinear Irreducible Characters

1989 ◽  
Vol 41 (1) ◽  
pp. 68-82 ◽  
Author(s):  
I. M. Isaacs
Keyword(s):  
Finite Groups ◽  
Irreducible Character ◽  
Group Actions ◽  
Character Degrees ◽  
Prime Divisors ◽  
Irreducible Characters ◽  
Nilpotent Length ◽  
Derived Subgroup ◽  
Nonlinear Irreducible Character

The main result of this paper is the following:Theorem A. Let H and N be finite groups with coprime orders andsuppose that H acts nontrivially on N via automorphisms. Assume that Hfixes every nonlinear irreducible character of N. Then the derived subgroup ofN is nilpotent and so N is solvable of nilpotent length≦ 2.Why might one be interested in a situation like this? There has been considerable interest in the question of what one can deduce about a group Gfrom a knowledge of the setcd(G) = ﹛x(l)lx ∈ Irr(G) ﹜of irreducible character degrees of G.Recently, attention has been focused on the prime divisors of the elements of cd(G). For instance, in [9], O. Manz and R. Staszewski consider π-separable groups (for some set π of primes) with the property that every element of cd(G) is either a 77-number or a π'-number.

Inequivalent, bordant group actions on a surface

1986 ◽  
Vol 99 (2) ◽  
pp. 233-238 ◽  
Author(s):  
Charles Livingston
Keyword(s):  
Fixed Point ◽  
Finite Groups ◽  
Group Actions ◽  
Free Actions ◽  
Orientable Surfaces

An action of a group, G, on a surface, F, consists of a homomorphismø: G → Homeo (F).We will restrict our discussion to finite groups acting on closed, connected, orientable surfaces, with ø(g) orientation-preserving for all g ε G. In addition we will consider only effective (ø is injective) free actions. Free means that ø(g) is fixed-point-free for all g ε G, g ≠ 1. This paper addresses the classification of such actions.

scholarly journals Extending group actions by finite groups. I

Topology ◽  
1992 ◽  
Vol 31 (2) ◽  
pp. 407-420 ◽  
Author(s):  
F.E.A. Johnson
Keyword(s):  
Finite Groups ◽  
Group Actions

scholarly journals Finite, Fiber- and Orientation-Preserving Group Actions on Totally Orientable Seifert Manifolds

2019 ◽  
Vol 33 (1) ◽  
pp. 235-265
Author(s):  
Benjamin Peet
Keyword(s):  
Finite Groups ◽  
General Structure ◽  
Group Actions ◽  
Base Space ◽  
Seifert Manifold ◽  
Seifert Manifolds ◽  
Obstruction Class ◽  
The Given

AbstractIn this paper we consider the finite groups that act fiber- and orientation-preservingly on closed, compact, and orientable Seifert manifolds that fiber over an orientable base space. We establish a method of constructing such group actions and then show that if an action satisfies a condition on the obstruction class of the Seifert manifold, it can be derived from the given construction. The obstruction condition is refined and the general structure of the finite groups that act via the construction is provided.

scholarly journals Reconstructing a minimal topological dynamical system from a set of return times

2021 ◽  
pp. 1-17
Author(s):  
KAMIL BULINSKI ◽  
ALEXANDER FISH
Keyword(s):  
Dynamical System ◽  
Finite Groups ◽  
Homogeneous Spaces ◽  
Group Actions ◽  
Transitive Group ◽  
Topological Dynamical System ◽  
Return Times ◽  
Open Set ◽  
Minimal Dynamical System

Abstract We investigate to what extent a minimal topological dynamical system is uniquely determined by a set of return times to some open set. We show that in many situations, this is indeed the case as long as the closure of this open set has no non-trivial translational symmetries. For instance, we show that under this assumption, two Kronecker systems with the same set of return times must be isomorphic. More generally, we show that if a minimal dynamical system has a set of return times that coincides with a set of return times to some open set in a Kronecker system with translationarily asymmetric closure, then that Kronecker system must be a factor. We also study similar problems involving nilsystems and polynomial return times. We state a number of questions on whether these results extend to other homogeneous spaces and transitive group actions, some of which are already interesting for finite groups.

scholarly journals Group actions on quiver varieties and applications

2019 ◽  
Vol 30 (02) ◽  
pp. 1950007 ◽  
Author(s):  
Victoria Hoskins ◽  
Florent Schaffhauser
Keyword(s):  
Finite Groups ◽  
Moduli Spaces ◽  
Group Actions ◽  
Group Cohomology ◽  
Quiver Representations ◽  
Quiver Varieties ◽  
Algebraic Actions

We study algebraic actions of finite groups of quiver automorphisms on moduli spaces of quiver representations. We decompose the fixed loci using group cohomology and we give a modular interpretation of each component. As an application, we construct branes in hyperkähler quiver varieties, as fixed loci of such actions.

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