A complex semigroup approach to group algebras of infinite dimensional Lie groups

TL;DR

This paper introduces a new approach to constructing host algebras for infinite dimensional Lie groups using complex involutive semigroups, linking algebraic structures with geometric properties of the Lie group's dual.

Contribution

It develops a framework based on complex semigroups to build host algebras for infinite dimensional Lie groups, extending the theory to non-commutative cases.

Findings

Constructs C^*-algebras from complex involutive semigroups.

Establishes a correspondence between host algebras and convex geometric sets in dual Lie algebra.

Describes all host algebras for additive groups of locally convex spaces.

Abstract

A host algebra of a topological group G is a C^*-algebra whose representations are in one-to-one correspondence with certain continuous unitary representations of G. In this paper we present an approach to host algebras for infinite dimensional Lie groups which is based on complex involutive semigroups. Any locally bounded absolute value \alpha on such a semigroup S leads in a natural way to a C^*-algebra C^*(S,\alpha), and we describe a setting which permits us to conclude that this C^*-algebra is a host algebra for a Lie group G. We further explain how to attach to any such host algebra an invariant weak-*-closed convex set in the dual of the Lie algebra of G enjoying certain nice convex geometric properties. If G is the additive group of a locally convex space, we describe all host algebras arising this way. The general non-commutative case is left for the future.