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1-amenability of 𝒜(X) for Banach spaces with 1-unconditional bases

A. Blanco (2012)

Studia Mathematica

The main result of the note is a characterization of 1-amenability of Banach algebras of approximable operators for a class of Banach spaces with 1-unconditional bases in terms of a new basis property. It is also shown that amenability and symmetric amenability are equivalent concepts for Banach algebras of approximable operators, and that a type of Banach space that was long suspected to lack property 𝔸 has in fact the property. Some further ideas on the problem of whether or not amenability (in...

2-local Jordan automorphisms on operator algebras

Ajda Fošner (2012)

Studia Mathematica

We investigate 2-local Jordan automorphisms on operator algebras. In particular, we show that every 2-local Jordan automorphism of the algebra of all n× n real or complex matrices is either an automorphism or an anti-automorphism. The same is true for 2-local Jordan automorphisms of any subalgebra of ℬ which contains the ideal of all compact operators on X, where X is a real or complex separable Banach spaces and ℬ is the algebra of all bounded linear operators on X.

2-summing multiplication operators

Dumitru Popa (2013)

Studia Mathematica

Let 1 ≤ p < ∞, = ( X ₙ ) n ∈ ℕ be a sequence of Banach spaces and l p ( ) the coresponding vector valued sequence space. Let = ( X ₙ ) n ∈ ℕ , = ( Y ₙ ) n ∈ ℕ be two sequences of Banach spaces, = ( V ₙ ) n ∈ ℕ , Vₙ: Xₙ → Yₙ, a sequence of bounded linear operators and 1 ≤ p,q < ∞. We define the multiplication operator M : l p ( ) → l q ( ) by M ( ( x ₙ ) n ∈ ℕ ) : = ( V ₙ ( x ₙ ) ) n ∈ ℕ . We give necessary and sufficient conditions for M to be 2-summing when (p,q) is one of the couples (1,2), (2,1), (2,2), (1,1), (p,1), (p,2), (2,p), (1,p), (p,q); in the last case 1 < p < 2, 1 < q < ∞.

(Non-)amenability of ℬ(E)

Volker Runde (2010)

Banach Center Publications

In 1972, the late B. E. Johnson introduced the notion of an amenable Banach algebra and asked whether the Banach algebra ℬ(E) of all bounded linear operators on a Banach space E could ever be amenable if dim E = ∞. Somewhat surprisingly, this question was answered positively only very recently as a by-product of the Argyros-Haydon result that solves the “scalar plus compact problem”: there is an infinite-dimensional Banach space E, the dual of which is ℓ¹, such that ℬ ( E ) = ( E ) + ℂ i d E . Still, ℬ(ℓ²) is not amenable,...

*-Representations, seminorms and structure properties of normed quasi *-algebras

Camillo Trapani (2008)

Studia Mathematica

The class of *-representations of a normed quasi *-algebra (𝔛,𝓐₀) is investigated, mainly for its relationship with the structure of (𝔛,𝓐₀). The starting point of this analysis is the construction of GNS-like *-representations of a quasi *-algebra (𝔛,𝓐₀) defined by invariant positive sesquilinear forms. The family of bounded invariant positive sesquilinear forms defines some seminorms (in some cases, C*-seminorms) that provide useful information on the structure of (𝔛,𝓐₀) and on the continuity...

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