Tensor Product of Distributive Sequential Effect Algebras and Product Effect Algebras

A distributive sequential effect algebra (DSEA) is an effect algebra on which a distributive sequential product with natural properties is defined. We define the tensor product of two arbitrary DSEA’s and we give a necessary and sufficient condition for it to exist. As a corollary we obtain the result (see Gudder, S. in Math. Slovaca 54:1–11, 2004, to appear) that the tensor product of a pair of commutative sequential effect algebras exists if and only if they admit a bimorphism. We further obtain a similar result for the tensor product of a pair of product effect algebras.     

Sequential Product of Quantum Effects: An Overview

This article presents an overview for the theory of sequential products of quantum effects. We first summarize some of the highlights of this relatively recent field of investigation and then provide some new results. We begin by discussing sequential effect algebras which are effect algebras endowed with a sequential product satisfying certain basic conditions. We then consider sequential products of (discrete) quantum measurements. We next treat transition effect matrices (TEMs) and their associated sequential product. A TEM is a matrix whose entries are effects and whose rows form quantum measurements. We show that TEMs can be employed for the study of quantum Markov chains. Finally, we prove some new results concerning TEMs and vector densities.     

The Brooks-Jewett Theorem on Effect Algebras with the Sequential Completeness Property

In this paper, we show that the Brooks-Jewett theorem on effect algebras with the sequential completeness property is valid.     

Uniqueness and Order in Sequential Effect Algebras

A sequential effect algebra (SEA) is an effect algebra on which a sequential product is defined. We present examples of effect algebras that admit a unique, many and no sequential product. Some general theorems concerning unique sequential products are proved. We discuss sequentially ordered SEAs in which the order is completely determined by the sequential product. It is demonstrated that intervals in a sequential ordered SEA admit a sequential product.     

Examples,problems, and results in effect algebras

This article discusses various unsolved problems and conjectures that have arisen in the study of effect algebras (orD-posets) during the last few years. We also include some examples, counterexamples, and results that motivate or partially solve these problems. The problems mainly concern sharp and principal elements, the existence of infima in Hilbert space effect algebras, tensor products, and interval algebras.     

Tensor Products of Quantum Structures and Their Applications in Quantum Measurements

Tensor products of quantum logics and effect algebras with some known problems are reviewed. It is noticed that although tensor products of effect algebras having at least one state exist, in the category of complex Hilbert space effect algebras similar problems as with tensor products of projection lattices occur. Nevertheless, if one of the two coupled physical systems is classical, tensor product exists and can be considered as a Boolean power. Some applications of tensor products (in the form of Boolean powers) to quantum measurements are reviewed.     

Kite Pseudo Effect Algebras

We define a new class of pseudo effect algebras, called kite pseudo effect algebras, which is connected with partially ordered groups not necessarily with strong unit. In such a case, starting even with an Abelian po-group, we can obtain a noncommutative pseudo effect algebra. We show how such kite pseudo effect algebras are tied with different types of the Riesz Decomposition Properties. Kites are so-called perfect pseudo effect algebras, and we define conditions when kite pseudo effect algebras have the least non-trivial normal ideal.     

Weak Commutative Pseudoeffect Algebras

As noncommutative generalizations of effect algebras, we introduce weak commutative pseudoeffect algebras. In this paper, we prove that the generalized pseudoeffect algebras can be unitized if and only if they are weak commutative. Then we discuss the relationships between weak commutative pseudoeffect algebras and weak commutative generalized pseudoeffect algebras. We prove that the category of weak commutative pseudoeffect algebras is a reflective subcategory of weak commutative generalized pseudoeffect algebras. Similarly, we introduce weak commutative pseudodifference posets and show the relationships between weak commutative pseudoeffect algebras and weak commutative pseudodifference posets.     

Subdirect Decompositions of Lattice Effect Algebras

We prove a theorem about subdirect decompositions of lattice effect algebras. Further, we show how, under these decompositions, blocks, sets of sharp elements and centers of those effects algebras are decomposed. As an application we prove a statement about the existence of subadditive state on some block-finite effect algebras.     

Pseudoeffect Algebras. I. Basic Properties

As a noncommutative generalization of effect algebras, we introduce pseudoeffect algebras and list some of their basic properties. For the purpose of a structure theory, we further define several kinds of Riesz-like properties for pseudoeffect algebras and show how they are interrelated.     

Atomic Effect Algebras with the Riesz Decomposition Property

We discuss the relationships between effect algebras with the Riesz Decomposition Property and partially ordered groups with interpolation. We show that any σ-orthocomplete atomic effect algebra with the Riesz Decomposition Property is an MV-effect algebras, and we apply this result for pseudo-effect algebras and for states.     

Pre-ideals of Basic Algebras

Basic algebras are a generalization of MV-algebras, also including orthomodular lattices and lattice effect algebras. A pre-ideal of a basic algebra is a non-empty subset that is closed under the addition ⊕ and downwards closed with respect to the underlying order. In this paper, we study the pre-ideal lattices of algebras in a particular subclass of basic algebras which are closer to MV-algebras than basic algebras in general. We also prove that finite members of this subclass are exactly finite MV-algebras.     

The Continuities of Nonadditive Functions on Effect Algebras

In this paper, we study the strongly continuities, monotone autocontinuities of functions defined on effect algebras from above and below, respectively, we also present some examples to show that the autocontinuity, order continuity and monotone autocontinuity of functions defined on effect algebras are different each other.     

Mixture Preserving Maps on Von Neumann Algebra Effects

In this paper we determine the structure of all bijective maps between the effect algebras of different von Neumann algebras which preserve mixtures in both directions. In particular, we obtain that every such preserver is a mixture isomorphism.      

Product Effect Algebras

We introduce a product on an effect algebra. We prove that every product effect algebra with the Riesz decomposition property (RDP), is an interval in an Abelian unital interpolation po-ring, and we show that the category of product effect algebras with the RDP is categorically equivalent with the category of unital Abelian interpolation po-rings. In addition, we show that every product effect algebra with the RDP and with 1 as a product unity is a subdirect product of antilattice product effect algebras with the RDP.     

Coproducts of D-Posets and Their Application to Probability

D-posets introduced by F. Chovanec and F. Kôpka ten years ago provide a suitable algebraic structure to model events in probability theory. Generalizing analogous results for fields of sets and bold algebras, we describe a duality between certain coproducts of D-posets and generalized measurable spaces. An important role in the duality is played by sequential convergence. We mention some applications to the foundations of probability.     

Integrable ODEs on Associative Algebras

In this paper we give definitions of basic concepts such as symmetries, first integrals, Hamiltonian and recursion operators suitable for ordinary differential equations on associative algebras, and in particular for matrix differential equations. We choose existence of hierarchies of first integrals and/or symmetries as a criterion for integrability and justify it by examples. Using our componentless approach we have solved a number of classification problems for integrable equations on free associative algebras. Also, in the simplest case, we have listed all possible Hamiltonian operators of low order. Received: 22 September 1999 / Accepted: 17 November 1999     

Anti-BZ-Structure in Effect Algebras

The definitions of sharply approximating effect algebras, anti-BZ-effect algebras, central approximating effect algebras, and S-anti-BZ-effect algebras are given, the relationships between sharply approximating effect algebras and anti-BZ-effect algebras, between central approximating effect algebras and anti-BZ-effect algebras are established, and the set of anti-BZ-sharp elements in S-anti-BZ-effect algebras is proved to be an orthomodular lattice.     

Global Geometric Deformations of the Virasoro Algebra,Current and Affine Algebras by Krichever–Novikov Type Algebras

In two earlier articles we constructed algebraic-geometric families of genus one (i.e. elliptic) Lie algebras of Krichever–Novikov type. The considered algebras are vector fields, current and affine Lie algebras. These families deform the Witt algebra, the Virasoro algebra, the classical current, and the affine Kac–Moody Lie algebras respectively. The constructed families are not equivalent (not even locally) to the trivial families, despite the fact that the classical algebras are formally rigid. This effect is due to the fact that the algebras are infinite dimensional. In this article the results are reviewed and developed further. The constructions are induced by the geometric process of degenerating the elliptic curves to singular cubics. The algebras are of relevance in the global operator approach to the Wess–Zumino–Witten–Novikov models appearing in the quantization of Conformal Field Theory.     

Existence of States on Pseudoeffect Algebras

Pseudoeffect (PE) algebras have been introduced as a noncommutative generalization of effect algebras. We study in this paper PE algebras with the special property of having a nonempty state space. To this end, we consider PE algebras which are po-group intervals and which are, in a certain sense, noncommutative only in the small. Such a PE algebra is shown to possess a nontrivial commutative homomorphic image from which then follows that there exist states. A typical example is given by an interval of the lexicographical product of two po-groups the first of which is abelian.