Abstract:Abstract. We study the Arens regularity of module actions of Banach left or right modules over Banach algebras. We prove that if A has a brai (blai), then the right (left) module action of A on A * is Arens regular if and only if A is reflexive. We find that Arens regularity is implied by the factorization of A * or A * * when A is a left or a right ideal in A * * . The Arens regularity and strong irregularity of A are related to those of the module actions of A on the nth dual A (n) of A. Banach algebras A fo… Show more
“…We can also prove Theorem 2.4 by applying Corollary 2.1. In fact, the conditions imposed on A imply that A is Arens regular (see [12,Theorem 4.3]). Furthermore, it is not difficult to check in this case that every derivation D : A → A * satisfies D ′′ (A * * ) ⊆ A * .…”
Section: This Is True If and Only If For Everymentioning
“…We can also prove Theorem 2.4 by applying Corollary 2.1. In fact, the conditions imposed on A imply that A is Arens regular (see [12,Theorem 4.3]). Furthermore, it is not difficult to check in this case that every derivation D : A → A * satisfies D ′′ (A * * ) ⊆ A * .…”
Section: This Is True If and Only If For Everymentioning
Let A and A be Banach algebras such that A is a Banach A-bimodule with compatible actions. We define the product A ⋊ A, which is a strongly splitting Banach algebra extension of A by A. After characterization of the multiplier algebra, topological centre, (maximal) ideals and spectrum of A ⋊ A, we restrict our investigation to the study of semisimplicity, regularity, Arens regularity of A ⋊ A in relation to that of the algebras A, A and the action of A on A. We also compute the first cohomology group H 1 (A ⋊ A, (A ⋊ A) (n) ) for all n ∈ N ∪ {0} as well as the first-order cyclic cohomology group H 1 λ (A ⋊ A, (A ⋊ A) (1) ), where (A ⋊ A) (n) is the n-th dual space of A ⋊ A when n ∈ N and A ⋊ A itself when n = 0. These results are not only of interest in their own right, but also they pave the way for obtaining some new results for Lau products and module extensions of Banach algebras as well as triangular Banach algebra. Finally, special attention is devoted to the cyclic and n-weak amenability of A ⋊ A.Mathematics Subject Classification (2010). 46H20, 46H25, 46H10, 47B48, 47B47, 16E40.
Abstract. Let A and B be Banach algebras, θ : A → B be a continuous Banach algebra homomorphism and I be a closed ideal in B. Then the direct sum of A and I with respect to θ, denoted A ⊲⊳ θ I, with a special product becomes a Banach algebra which is called the amalgamated Banach algebra. In this paper, among other things, we compute the topological centre of A ⊲⊳ θ I in terms of that of A and I. Using this, we provide a characterization of the Arens regularity of A ⊲⊳ θ I. Then we determine the character space of A ⊲⊳ θ I in terms of that of A and I. Moreover, we study the weak amenability of A ⊲⊳ θ I.
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