Almost homomorphisms of compact groups

Almost commuting elements in compact Lie groups

Compact Homomorphisms of (t-algebras

Suppose A is a C*-algebra and B is a Banach algebra such that it can be continuously imbedded in B(H), the Banach algebra of bounded linear operators on some Hubert space H. It is shown that if 6 is a compact algebra homomorphism from A into B, then 6 is a finite rank operator, and the range of 0 is spanned by a finite number of idempotents. If, moreover, B is commutative, then 9 has the form 8...

Half-homomorphisms of Groups

Let G and G' be multiplicative systems. A half-homomorphism of G into G' will mean a mapping a—>a' of G into C such that for all a, bEG, (ab)'=a'V or b'a'. An anti-homomorphism is a mapping such that always (ab)' = b'a'. The terms half-isomorphism, etc., are defined similarly. It will be shown that any half-homomorphism of a group G into a group G' is either a homomorphism or an anti-homomorphi...

Almost Unimodular Systems on Compact Groups with Disjoint Spectra

We emulate the Rademacher functions on any non-commutative compact group requiring the resulting system to have pairwise disjoint spectra. Introduction Let G be a compact topological group with normalized Haar measure μ and dual object Ĝ. Let π : G → U(Hπ) be an irreducible unitary representation of G. Then, given an integrable function f : G → C, the Fourier coefficient of f at π is defined as...

Homomorphisms between Diffeomorphism Groups

For r ≥ 3, p ≥ 2, we classify all actions of the groups Diffc(R) and Diff+(S) by Cdiffeomorphisms on the line and on the circle. This is the same as describing all nontrivial group homomorphisms between groups of compactly supported diffeomorphisms on 1-manifolds. We show that all such actions have an elementary form, which we call topologically diagonal. As an application, we answer a question...