Title: Locally Compact Contraction Groups

by Helge Glöckner (Universität Paderborn) as part of Topological Groups

Lecture held in Elysium.

Abstract

Consider a locally compact group $G$, together with an automorphism $alpha$ which is $contractive$ in the sense that $alpha^nrightarrow{rm id}_G$ pointwise as $ntoinfty$. Siebert showed that $G$ is the direct product of its connected component $G_e$ and an $alpha$-stable, totally disconnected closed subgroup;

moreover, $G_e$ is a simply connected, nilpotent real Lie group.

I’ll report on research concerning the totally disconnected part, obtained jointly with G. A. Willis.

For each totally disconnected contraction group $(G,alpha)$, the set ${rm tor} G$ of torsion elements is a closed subgroup of $G$. Moreover, $G$ is a direct product

$$G=G_{p_1}times cdotstimes G_{p_n}times {rm tor} G$$ of $alpha$-stable $p$-adic Lie groups $G_p$ for certain primes $p_1,ldots, p_n$ and the torsion subgroup. The structure of $p$-adic contraction groups is known from the work of J. S. P. Wang; notably, they are nilpotent. As shown with Willis, ${rm tor} G$ admits a composition series and there are countably many possible composition factors, parametrized by the finite simple groups. More recent research showed that there are uncountably many non-isomorphic torsion contraction groups, but only countably many abelian ones. If a torsion contraction group $G$ has a compact open subgroup which is a pro-$p$-group, then $G$ is nilpotent. Likewise if $G$ is locally pro-nilpotent.

Title: Group dualities: G-barrelled groups

by Elena Martín-Peinador (University of Madrid) as part of Topological Groups

Lecture held in Elysium.

Abstract

A natural notion in the framework of abelian groups are the group dualities. The most efficient definition of a group duality is simply a pair $(G, H)$, where $G$ denotes an abstract abelian group and $H$ a subgroup of characters of $G$, that is $H leq {rm Hom}(G, mathbb T)$. Two group topologies for $G$ and $H$ appear from scratch in a group duality $(G, H)$: the weak topologies $sigma(G, H)$ and $sigma (H, G)$ respectively. Are there more group topologies either in $G$ or $H$ that can be strictly related with the duality $(G, H)$? In this sense we shall define the term “compatible topology” and loosely speaking we consider the compatible topologies as members of the duality.

The locally quasi-convex topologies defined by Vilenkin in the 50′s form a significant class for the construction of a duality theory for groups. The fact that a locally convex topological vector space is in particular a locally quasi-convex group serves as a nexus to emulate well-known results of Functional Analysis for the class of topological groups.

In this talk we shall

deal with questions of the sort:

Under which conditions is there a locally compact topology in a fixed duality?

The same question for a metrizable, or a $k$-group topology.

We shall also introduce the $g$-barrelled groups, a class for which the Mackey-Arens Theorem admits an optimal counterpart. We study also the existence of $g$-barrelled topologies in a group duality $(G, H)$.

Title: Classification of Periodic LCA Groups of Finite Non-Archimedean Dimension

by Wayne Lewis (University of Hawaiʻi) as part of Topological Groups

Lecture held in Elysium.

Abstract

A periodic LCA group such that the $p$-components all have $p$-rank bounded above by a common positive integer are classified via a complete set of topological isomorphism invariants realized by an equivalence relation on pairs of extended supernatural vectors.

Remaining time will be devoted to a facilitated discussion on how things are going this fall/winter academic semester in your part of the world as you see it.

Title: The Semigroup $beta S$

by Dona Strauss (University of Leeds) as part of Topological Groups

Lecture held in Elysium.

Abstract

If $S$ is a discrete semigroup, the semigroup operation on $S$ can be extended to a semigroup operation on its Stone–Čech compactification $beta S$. The properties of the semigroup $beta S$ have been a powerful tool in topological dynamics and combinatorics.

I shall give an introductory description of the semigroup $beta S$, and show how its properties can be used to prove some of the classical theorems of Ramsey Theory.

Title: Closed Lie Ideals and Center of Generalized Group Algebras

by Bharat Talwar (University of Dehli) as part of Topological Groups

Lecture held in Elysium.

Abstract

The closed Lie ideals of the generalized group algebra $L^1(G,A)$ are characterized in terms of elements of the group $G$, elements of the algebra $A$, and the modular function $Delta$ of the group $G$. Conditions under which for a given closed Lie ideal $Lsubseteq A$ the subspace $L^1(G,L)$ is a Lie ideal, and vice versa, are discussed. The center of $L^1(G,A)$ is characterized, followed by a discussion regarding a very special projection in $L^1(G,A)$. Finally, a few restrictions are imposed on $G$ and $A$ under which $mathcal{Z}(L^1(G,A))congmathcal{Z}(L^1(G))otimes^gammamathcal{Z}(A)$.

The presentation is based on joint work with Ved Prakash Gupta and Ranjana Jain.

Title: Topologies, idempotents and ideals

by Nico Spronk (University of Waterloo) as part of Topological Groups

Lecture held in Elysium.

Abstract

Let $G$ be a topological group. I wish to exhibit a bijection between (i) a certain class of weakly almost periodic topologies, (ii) idempotents in the weakly almost periodic compactification of $G$, and (iii) certain ideals of the algebra of weakly almost periodic functions. This has applications to decomposing weakly almost periodic representations on Banach spaces, generalizing results which go back to many authors.

Moving to unitary representations, I will develop the Fourier-Stieltjes algebra $B(G)$ of $G$, and give the analogous result there. As an application, I show that for a locally compact connected group, operator amenability of $B(G)$ implies that $G$ is compact, partially resolving a problem of interest for 25 years.

Title: Potential Theory on Stratified Lie Groups

by Mukund Madhav Mishra (Hansraj College) as part of Topological Groups

Lecture held in Elysium.

Abstract

Stratified Lie groups form a special subclass of the class of nilpotent Lie groups. The Lie algebra of a stratified Lie group possesses a specific stratification (and hence the name), and an interesting class of anisotropic dilations. Among the linear differential operators of degree two, there exists a family that is well behaved with the automorphisms of the stratified Lie group, especially with the anisotropic dilations. We shall see that one such family of operators mimics the classical Laplacian in many aspects, except for the regularity. More specifically, these Laplace-like operators are sub-elliptic, and hence referred to as the sub-Laplacians. We will review certain interesting properties of functions harmonic with respect to the sub-Laplacian on a stratified Lie group, and have a closer look at a particular class of stratified Lie groups known as the class of Heisenberg type groups.

Title: Compact Quantum Groups and their Semidirect Products

by Sutanu Roy (National Institute of Science Education and Research) as part of Topological Groups

Lecture held in Elysium.

Abstract

Compact quantum groups are noncommutative analogs of compact groups in the realm of noncommutative geometry introduced by S. L. Woronowicz back in the 80s. Roughly, they are unital C*-bialgebras in the monoidal category (given by the minimal tensor product) of unital C*-algebras with some additional properties. For real 0<|q|<1, q-deformations of SU(2) group are the first and well-studied examples of compact quantum groups. These examples were constructed independently by Vaksman-Soibelman and Woronowicz also back in the 80s. In fact, they are examples of a particular class of compact quantum groups namely, compact matrix pseudogroups. The primary goal of this talk is to motivate and discuss some of the interesting aspects of this theory from the perspective of the compact groups. In the second part, I shall briefly discuss the semidirect product construction for compact quantum groups via an explicit example. The second part of this will be based on a joint work with Paweł Kasprzak, Ralf Meyer and Stanislaw Lech Woronowicz.