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Left quotients of a C*-algebra, III: Operators on left quotients

Lawrence G. Brown, Ngai-Ching Wong (2013)

Studia Mathematica

Let L be a norm closed left ideal of a C*-algebra A. Then the left quotient A/L is a left A-module. In this paper, we shall implement Tomita’s idea about representing elements of A as left multiplications: π p ( a ) ( b + L ) = a b + L . A complete characterization of bounded endomorphisms of the A-module A/L is given. The double commutant π p ( A ) ' ' of π p ( A ) in B(A/L) is described. Density theorems of von Neumann and Kaplansky type are obtained. Finally, a comprehensive study of relative multipliers of A is carried out.

Maps preserving zero products

J. Alaminos, M. Brešar, J. Extremera, A. 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...

M-complete approximate identities in operator spaces

A. Arias, H. Rosenthal (2000)

Studia Mathematica

This work introduces the concept of an M-complete approximate identity (M-cai) for a given operator subspace X of an operator space Y. M-cai’s generalize central approximate identities in ideals in C*-algebras, for it is proved that if X admits an M-cai in Y, then X is a complete M-ideal in Y. It is proved, using ’special’ M-cai’s, that if J is a nuclear ideal in a C*-algebra A, then J is completely complemented in Y for any (isomorphically) locally reflexive operator space Y with J ⊂ Y ⊂ A and...

Metric enrichment, finite generation, and the path coreflection

Alexandru Chirvasitu (2024)

Archivum Mathematicum

We prove a number of results involving categories enriched over CMet, the category of complete metric spaces with possibly infinite distances. The category CPMet of path complete metric spaces is locally ℵ 1 -presentable, closed monoidal, and coreflective in CMet. We also prove that the category CCMet of convex complete metric spaces is not closed monoidal and characterize the isometry- ℵ 0 -generated objects in CMet, CPMet and CCMet, answering questions by Di Liberti and Rosický. Other results include...

Moore-Penrose inverses of Gram operators on Hilbert C*-modules

M. S. Moslehian, K. Sharif, M. Forough, M. Chakoshi (2012)

Studia Mathematica

Let t be a regular operator between Hilbert C*-modules and t † be its Moore-Penrose inverse. We investigate the Moore-Penrose invertibility of the Gram operator t*t. More precisely, we study some conditions ensuring that t † = ( t * t ) † t * = t * ( t t * ) † and ( t * t ) † = t † t * † . As an application, we get some results for densely defined closed operators on Hilbert C*-modules over C*-algebras of compact operators.

Morita equivalence of groupoid C*-algebras arising from dynamical systems

Xiaoman Chen, Chengjun Hou (2002)

Studia Mathematica

We show that the stable C*-algebra and the related Ruelle algebra defined by I. Putnam from the irreducible Smale space associated with a topologically mixing expanding map of a compact metric space are strongly Morita equivalent to the groupoid C*-algebras defined directly from the expanding map by C. Anantharaman-Delaroche and V. Deaconu. As an application, we calculate the K⁎-group of the Ruelle algebra for a solenoid.

Nice connecting paths in connected components of sets of algebraic elements in a Banach algebra

Endre Jr. Makai, Jaroslav Zemánek (2016)

Czechoslovak Mathematical Journal

Generalizing earlier results about the set of idempotents in a Banach algebra, or of self-adjoint idempotents in a C * -algebra, we announce constructions of nice connecting paths in the connected components of the set of elements in a Banach algebra, or of self-adjoint elements in a C * -algebra, that satisfy a given polynomial equation, without multiple roots. In particular, we prove that in the Banach algebra case every such non-central element lies on a complex line, all of whose points satisfy the...

Non-commutative Gelfand-Naimark theorem

Janusz Migda (1993)

Commentationes Mathematicae Universitatis Carolinae

We show that if Y is the Hausdorffization of the primitive spectrum of a C * -algebra A then A is * -isomorphic to the C * -algebra of sections vanishing at infinity of the canonical C * -bundle over Y .

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