Spectral Invariance of Dense Subalgebras of Operator Algebras

TL;DR

This paper introduces strong spectral invariance for dense subalgebras of operator algebras and proves spectral invariance of crossed products for certain Lie groups, with applications to dynamical systems.

Contribution

It establishes strong spectral invariance for dense Frechet subalgebras in C*-algebras and demonstrates spectral invariance of crossed products for specific Lie groups.

Findings

Spectral invariance of G times A for polynomial growth Lie groups.

Examples include finitely generated groups and nilpotent Lie groups.

Applications to spectral invariant subalgebras in dynamical systems.

Abstract

We define the notion of strong spectral invariance for a dense Frechet subalgebra A of a Banach algebra B. We show that if A is strongly spectral invariant in a C*-algebra B, and G is a compactly generated polynomial growth Type R Lie group, not necessarily connected, then the smooth crossed product G\rtimes A is spectral invariant in the C*-crossed product G\rtimes B. Examples of such groups are given by finitely generated polynomial growth discrete groups, compact or connected nilpotent Lie groups, the group of Euclidean motions on the plane, the Mautner group, or any closed subgroup of one of these. Our theorem gives the spectral invariance of G\rtimes A if A is the set of C^{\infty}-vectors for the action of G on B, or if B= C_{0}(M), and A is a set of G-differentiable Schwartz functions S(M) on M. This gives many examples of spectral invariant dense subalgebras for the C*-algebras associated with dynamical systems. We also obtain relevant results about exact sequences, subalgebras, tensoring by smooth compact operators, and strong spectral invariance in L_{1}(G, B).