Wyniki wyszukiwania

Sortuj według:

Ogranicz wyniki do:

Convolutions on compact groups and Fourier algebras of coset spaces

100%

Forrest B., Samei E., Spronk N.

Studia Mathematica

2010

tom 196

nr 3

223-249

We study two related questions. (1) For a compact group G, what are the ranges of the convolution maps on A(G × G) given for u,v in A(G) by u × v ↦ u*v̌ (v̌(s) = v(s^-1)) and u × v ↦ u*v? (2) For a locally compact group G and a compact subgroup K, what are the amenability properties of the Fourier algebra of the coset space A(G/K)? The algebra A(G/K) was defined and studied by the first named author. In answering the first question, we obtain, for compact groups which do not admit an abelian subgroup of finite index, some new subalgebras of A(G). Using those algebras we can find many instances in which A(G/K) fails the most rudimentary amenability property: operator weak amenability. However, using different techniques, we show that if the connected component of the identity of G is abelian, then A(G/K) always satisfies the stronger property that it is hyper-Tauberian, which is a concept developed by the second named author. We also establish a criterion which characterises operator amenability of A(G/K) for a class of groups which includes the maximally almost periodic groups. Underlying our calculations are some refined techniques for studying spectral synthesis properties of sets for Fourier algebras. We even find new sets of synthesis and nonsynthesis for Fourier algebras of some classes of groups.

Operator Segal algebras in Fourier algebras

100%

Forrest B., Spronk N., Wood P.

Studia Mathematica

2007

tom 179

nr 3

277-295

Let G be a locally compact group, A(G) its Fourier algebra and L¹(G) the space of Haar integrable functions on G. We study the Segal algebra S¹A(G) = A(G) ∩ L¹(G) in A(G). It admits an operator space structure which makes it a completely contractive Banach algebra. We compute the dual space of S¹A(G). We use it to show that the restriction operator $u ↦ u|_{H}: S¹A(G) → A(H)$, for some non-open closed subgroups H, is a surjective complete quotient map. We also show that if N is a non-compact closed subgroup, then the averaging operator $τ_{N}: S¹A(G) → L¹(G/N)$, $τ_{N}u(sN) = ∫_{N} u(sn)dn$, is a surjective complete quotient map. This puts an operator space perspective on the philosophy that S¹A(G) is "locally A(G) while globally L¹". Also, using the operator space structure we can show that S¹A(G) is operator amenable exactly when when G is compact; and we can show that it is always operator weakly amenable. To obtain the latter fact, we use E. Samei's theory of hyper-Tauberian Banach algebras.

Ograniczanie wyników

2 Studia Mathematica

2 Forrest B.

2 Spronk N.

1 Samei E.

1 Wood P.

1 2010

1 2007

Wyniki wyszukiwania

Convolutions on compact groups and Fourier algebras of coset spaces

Operator Segal algebras in Fourier algebras