Some Notes on Semidirect Products of Banach Algebras

Abstract

Let A and U be Banach algebras such that U is also a Banach Abimodule with compatible algebra operations, module actions and norm. By defining an approprite action, we turn l 1 -direct product A × U into a Banach algebra such that A is closed subalgebra and U is a closed ideal of it. This algebra, is in fact semidirect product of A and U which we denote it by A ⋉ U and every semidirect products of Banach algebras can be represented as this form. In this paper we consider the Banach algebra A ⋉ U as mentioned and study the derivations on it. In fact we consider the automatic continuity of the derivations on A ⋉ U and obtain some results in this context and study its relation with the automatic continuity of the derivations on A and U . Also we calculate the first cohomology group of A ⋉ U in some different cases and establish relations among the first cohomology group of A ⋉ U and those of A and U . As applications of these contents, we present various results about the automatic continuity of derivations and the first cohomology group of direct products of Banach algebras, module extension Banach algebras and θ-Lau products of Banach algebras. MSC(2010): 16E40; 46H40; 46H25.

The Product Between Three Banach Algebras

“…Many researchers have become interested in this subject and have worked on it. See [14,6] for more reading. In [4] we define (α, β) -product by the following identity, where α, β ∈ Hom(A, B)…”

On automatic continuity of the derivations on module extension of Banach algebras

“…See also [4,15] where the continuity of the derivations are studied on certain rpoducts of Banach algebras. Some results on the derivations and Jordan derivations on trivial extension and triangular Banach algebras have been established by in a number of papers; see [4][5][6][7][8][9][10][11][12][13][14] Let A be a Banach algebra and U be a Banach A-bimodule. The module extension or trivial extension Banach algebra associated to A and U, denoted by T (A, U), is the ℓ 1 -direct sum A ⊕ U equipped with the algebra multiplication given by (a, u…”