Associative and Lie algebras of quotients

In this paper we examine how the notion of algebra of quotients for Lie algebras ties up with the corresponding well-known concept in the associative case. Specifically, we completely characterize when a Lie algebra Q is an algebra of quotients of a Lie algebra L in terms of the associative algebras generated by the adjoint operators of L and Q respectively. In a converse direction, we also provide with new examples of algebras of quotients of Lie algebras and these come from associative algebras of quotients. In the course of our analysis, we make use of the notions of density and multiplicative semiprimeness to link our results with the maximal symmetric ring of quotients

Real rank zero algebras have the corona factorization property

The purpose of this short note is to prove that a stable separable C*-algebra with real rank zero has the so-called corona factorization property, that is, all the full multiplier projections are properly in finite. Enroute to our result, we consider conditions under which a real rank zero C*-algebra admits an injection of the compact operators (a question already considered in [21])

Recovering the Elliott invariant from the Cuntz semigroup

Let $A$ be a simple, separable C$^*$-algebra of stable rank one. We prove that the Cuntz semigroup of \CC(\T,A) is determined by its Murray-von Neumann semigroup of projections and a certain semigroup of lower semicontinuous functions (with values in the Cuntz semigroup of $A$). This result has two consequences. First, specializing to the case that $A$ is simple, finite, separable and $\mathcal Z$-stable, this yields a description of the Cuntz semigroup of \CC(\T,A) in terms of the Elliott invariant of $A$. Second, suitably interpreted, it shows that the Elliott functor and the functor defined by the Cuntz semigroup of the tensor product with the algebra of continuous functions on the circle are naturally equivalent.Comment: 16 page

Strongly non-degenerate Lie algebras

Let A be a semiprime 2 and 3-torsion free non-commutative associative algebra. We show that the Lie algebra Der(A) of(associative) derivations of A is strongly non-degenerate, which is a strong form of semiprimeness for Lie algebras, under some additional restrictions on the center of A. This result follows from a description of the quadratic annihilator of a general Lie algebra inside appropriate Lie overalgebras. Similar results are obtained for an associative algebra A with involution and the Lie algebra SDer(A) of involution preserving derivations of

RECASTING THE ELLIOTT CONJECTURE

Let A be a simple, unital, finite, and exact C*-algebra which absorbs the Jiang-Su algebra Z tensorially. We prove that the Cuntz semigroup of A admits a complete order embedding into an ordered semigroup which is obtained from the Elliott invariant in a functorial manner. We conjecture that this embedding is an isomor phism, and prove the conjecture in several cases. In these same cases - Z-stable algebras all - we prove that the Elliott conjecture in its strongest form is equivalent to a conjecture which appears much weaker. Outside the class of Z-stable C*-algebras, this weaker conjecture has no known counterexamples, and it is plausible that none exist. Thus, we reconcile the still intact principle of Elliott's classification conjecture -that K-theoretic invariants will classify separable and nuclear C*-algebras- with the recent appearance of counterexamples to its strongest concrete form

The Cuntz semigroup, the Elliott conjecture, and dimension functions on C*-Algebras

We prove that the Cuntz semigroup is recovered functorially from the Elliott invariant for a large class of C¤-algebras. In particular, our results apply to the largest class of simple C¤-algebras for which K-theoretic classification can be hoped for. This work has three significant consequences. First, it provides new conceptual insight into Elliott's classification program, proving that the usual form of the Elliott conjecture is equivalent, among Z-stable algebras, to a conjecture which is in general substantially weaker and for which there are no known counterexamples. Second and third, it resolves, for the class of algebras above, two conjectures of Blackadar and Handelman concerning the basic structure of dimension functions on C¤-algebras. We also prove in passing that the Kuntz-Pedersen semigroup is recovered functorially from the Elliott invariant for all simple unital C¤-algebras of interest

Recovering the Elliott invariant from the Cuntz semigroup

Let A be a simple, separable C*-algebra of stable rank one. We prove that the Cuntz semigroup of C (T, A) is determined by its Murray-von Neumann semigroup of projections and a certain semigroup of lower semicontinuous functions (with values in the Cuntz semigroup of A). This result has two consequences. First, specializing to the case that A is simple, finite, separable and Z-stable, this yields a description of the Cuntz semigroup of C (T, A) in terms of the Elliott invariant of A. Second, suitably interpreted, it shows that the Elliott functor and the functor defined by the Cuntz semigroup of the tensor product with the algebra of continuous functions on the circle are naturally equivalent

Chain conditions for Leavitt path algebras

In this paper, results known about the artinian and noetherian conditions for the Leavitt path algebras of graphs with finitely many vertices are extended to all row-finite graphs. In our first main result, necessary and sufficient conditions on a row-finite graph E are given so that the corresponding (not necessarily unital) Leavitt path K-algebra L(E) is semisimple. These are precisely the algebras L(E)for which every corner is left (equivalently, right)artinian. They are also precisely the algebras L(E) for which every finitely generated left (equivalently, right) L(E)-module is artinian. In our second main result, we give necessary and sufficient conditions for every corner of L(E) to be left (equivalently, right) noetherian. They also turn out to be precisely those algebras L(E) for which every finitely generated left(equivalently, right) L(E)-module is noetherian. In both situations, isomorphisms between these algebras and appropriate direct sums of matrix rings over K or K[x, x−1] are provided. Likewise, in both situations, equivalent graph theoretic conditions on E are presented

Teoria-K no estable per a anells de multiplicadors

Descripció del recurs: el 20-08-2008Consultable des del TDXTítol obtingut de la portada digitalitzadaEn esta Tesis damos una descripción del monoide V(M(A)) de clases de equivalencia de idempotentes/proyecciones de anillos de multiplicadores M(A), en el sentido de Murray-Von Neumann. Esta correspondencia se aplica principalmente a anillos de multiplicadores de anillos regulares simples y a una clase amplia de C*-álgebras simples con rango real cero y rango estable uno. Con esta descripción analizamos el reticulo de ideales del monoide V(M(A)), que por otro lado es un ingrediente crucial para entender la estructura de ideales del correspondiente anillo de multiplicadores. En casos importantes, demostramos que si A tiene escala finita, entonces el cociente de M(A) por cualquier ideal cerrado I que contiene propiamente a A, tiene rango estable uno. La extraordinaria complicación que presenta el retículo de ideales de M(A) se ve reflejada en el hecho que M(A) puede tener una cantidad no numerable de cocientes distintos. La metodologia desarrollada se aplica para el estudio de la riqueza de extremos en C*-álgebras. En particular, demostramos que el espacio de quasitrazas y la escala contienen suficiente información para decidir si M(A)/A tiene riqueza de extremos, lo que ocurre si la escala es finita. Si la escala no es finita, necesitamos condiciones más restrictivas

Teoria-K no estable per a anells de multiplicadors

En esta Tesis damos una descripción del monoide V(M(A)) de clases de equivalencia de idempotentes/proyecciones de anillos de multiplicadores M(A), en el sentido de Murray-Von Neumann. Esta correspondencia se aplica principalmente a anillos de multiplicadores de anillos regulares simples y a una clase amplia de C*-álgebras simples con rango real cero y rango estable uno. Con esta descripción analizamos el reticulo de ideales del monoide V(M(A)), que por otro lado es un ingrediente crucial para entender la estructura de ideales del correspondiente anillo de multiplicadores. En casos importantes, demostramos que si A tiene escala finita, entonces el cociente de M(A) por cualquier ideal cerrado I que contiene propiamente a A, tiene rango estable uno. La extraordinaria complicación que presenta el retículo de ideales de M(A) se ve reflejada en el hecho que M(A) puede tener una cantidad no numerable de cocientes distintos. La metodologia desarrollada se aplica para el estudio de la riqueza de extremos en C*-álgebras. En particular, demostramos que el espacio de quasitrazas y la escala contienen suficiente información para decidir si M(A)/A tiene riqueza de extremos, lo que ocurre si la escala es finita. Si la escala no es finita, necesitamos condiciones más restrictivas