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Derivations on Jordan-Banach algebras

A. Villena — 1996

Studia Mathematica

We establish that all derivations on a semisimple Jordan-Banach algebra are automatically continuous. By showing that "almost all" primitive ideals in the algebra are invariant under a given derivation, the general case is reduced to that of primitive Jordan-Banach algebras.

Operators determining the complete norm topology of C(K)

A. Villena — 1997

Studia Mathematica

For any uniformly closed subalgebra A of C(K) for a compact Hausdorff space K without isolated points and x 0 A , we show that every complete norm on A which makes continuous the multiplication by x 0 is equivalent to · provided that x 0 - 1 ( λ ) has no interior points whenever λ lies in ℂ. Actually, these assertions are equivalent if A = C(K).

Derivations with a hereditary domain, II

A. Villena — 1998

Studia Mathematica

The nilpotency of the separating subspace of an everywhere defined derivation on a Banach algebra is an intriguing question which remains still unsolved, even for commutative Banach algebras. On the other hand, closability of partially defined derivations on Banach algebras is a fundamental problem motivated by the study of time evolution of quantum systems. We show that the separating subspace S(D) of a Jordan derivation defined on a subalgebra B of a complex Banach algebra A satisfies B [ B S ( D ) ] B R a d B ( A ) provided...

Uniqueness of the topology on L¹(G)

J. ExtremeraJ. F. MenaA. R. Villena — 2002

Studia Mathematica

Let G be a locally compact abelian group and let X be a translation invariant linear subspace of L¹(G). If G is noncompact, then there is at most one Banach space topology on X that makes translations on X continuous. In fact, the Banach space topology on X is determined just by a single nontrivial translation in the case where the dual group Ĝ is connected. For G compact we show that the problem of determining a Banach space topology on X by considering translation operators on X is closely related...

Norm attaining bilinear forms on C*-algebras

J. AlaminosR. PayáA. R. Villena — 2003

Studia Mathematica

We give a sufficient condition on a C*-algebra to ensure that every weakly compact operator into an arbitrary Banach space can be approximated by norm attaining operators and that every continuous bilinear form can be approximated by norm attaining bilinear forms. Moreover we prove that the class of C*-algebras satisfying this condition includes the group C*-algebras of compact groups.

Maps preserving zero products

J. AlaminosM. BrešarJ. ExtremeraA. R. Villena — 2009

Studia Mathematica

A linear map T from a Banach algebra A into another B preserves zero products if T(a)T(b) = 0 whenever a,b ∈ A are such that ab = 0. This paper is mainly concerned with the question of whether every continuous linear surjective map T: A → B that preserves zero products is a weighted homomorphism. We show that this is indeed the case for a large class of Banach algebras which includes group algebras. Our method involves continuous bilinear maps ϕ: A × A → X (for some Banach space X) with the property...

Stability of commuting maps and Lie maps

J. AlaminosJ. ExtremeraŠ. ŠpenkoA. R. Villena — 2012

Studia Mathematica

Let A be an ultraprime Banach algebra. We prove that each approximately commuting continuous linear (or quadratic) map on A is near an actual commuting continuous linear (resp. quadratic) map on A. Furthermore, we use this analysis to study how close are approximate Lie isomorphisms and approximate Lie derivations to actual Lie isomorphisms and Lie derivations, respectively.

Lie triple ideals and Lie triple epimorphisms on Jordan and Jordan-Banach algebras

M. BrešarM. CabreraM. FošnerA. R. Villena — 2005

Studia Mathematica

A linear subspace M of a Jordan algebra J is said to be a Lie triple ideal of J if [M,J,J] ⊆ M, where [·,·,·] denotes the associator. We show that every Lie triple ideal M of a nondegenerate Jordan algebra J is either contained in the center of J or contains the nonzero Lie triple ideal [U,J,J], where U is the ideal of J generated by [M,M,M]. Let H be a Jordan algebra, let J be a prime nondegenerate Jordan algebra with extended centroid C and unital central closure Ĵ, and let...

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