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arXiv1995

Approximate Unitary Equivalence of Homomorphisms from O_infinity

We prove that if two nonzero homomorphisms from the Cuntz algebra O_infinity to a purely infinite simple C*-algebra have the same class in KK-theory, and if either both are unital or both are nonunital, then they are approximately unitarily equivalent. It follows that O_infinity is classifiable in the sense of Rordam. In particular, Rordam's classification theorem for direct limits of matrix algebras over even Cuntz algebras extends to direct limits involving both matrix algebras over even Cuntz algebras and corners of O_infinity for which the K_0 group can be an arbitrary countable abelian group with no even torsion.

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arXiv1995

Virtual Extensions

A process of extending sets which can be used as foundation for an alternative organization for Differential and Integral Calculus is presented.

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arXiv1995

Noncommutative flows I: dynamical invariants

We show that a noncommutative dynamical system of the type that occurs in quantum theory can often be associated with a dynamical principle; that is, an infinitesimal structure that completely determines the dynamics. The nature of these dynamical principles is similar to that of the second order differential equations of classical mechanics, in that one can locate a space of momentum operators, a ``Riemannian metric", and a potential. These structures are classified in terms of geometric objects which, in the simplest cases, occur in finite dimensional matrix algebras. As a consequence, we obtain a new classification of E_0-semigroups acting on type I factors.

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arXiv1996

Purely infinite simple $C^*$-algebras arising from free product constructions

Examples of simple, separable, unital, purely infinite $C^*$--algebras are constructed, including: (1) some that are not approximately divisible; (2) those that arise as crossed products of any of a certain class of $C^*$--algebras by any of a certain class of non--unital endomorphisms; (3) those that arise as reduced free products of pairs of $C^*$--algebras with respect to any from a certain class of states.

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arXiv1996

Asymptotic estimates for bound states in quantum waveguides coupled laterally through a narrow window

Consider the Laplacian in a straight planar strip of width $\,d\,$, with the Neumann boundary condition at a segment of length $\,2a\,$ of one of the boundaries, and Dirichlet otherwise. For small enough $\,a\,$ this operator has a single eigenvalue $\,ε(a)\,$; we show that there are positive $\,c_1,c_2\,$ such that $\,-c_1 a^4 \le ε(a)- \left(π/ d\right)^2 \le -c_2 a^4\,$. An analogous conclusion holds for a pair of Dirichlet strips, of generally different widths, with a window of length $\,2a\,$ in the common boundary.

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arXiv1996

Complex structure and solutions of classical nonlinear equation with the interaction $u^4_4$

We consider the (real) nonlinear wave equation $$\Box u + m^2 u + λu^3 = 0, \quad m > 0, \quad λ> 0, $$ on four-\-dimensional Minkowski space. We introduce the complex structure and show that the (nonlinear) operator of dynamics, the wave and scattering operators define complex analytic maps on the space of initial Cauchy data with finite energy. In other words, let $R(φ, π) = φ+ iμ^{-1}π$ be the map of initial data on the positive frequency part of the solution of the free Klein-\-Gordon equation with these initial data. The operators $RU(t)R^{-1},$ $RWR^{-1},$ and $RSR^{-1}$ are defined correctly and are complex analytic on the complex Hilbert space $H^1({\R}^3,\C).$

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arXiv1998

A Galois Correspondence for Compact Groups of Automorphisms of von Neumann Algebras with a Generalization to Kac Algebras

Let $M$ be a factor with separable predual and $G$ a compact group of automorphisms of $M$ whose action is minimal, i.e. $M^{G^\prime}\cap M = C$, where $M^G$ denotes the $G$-fixed point subalgebra. Then every intemediate von Neumann algebra $M^G\subset N\subset M$ has the form $N=M^H$ for some closed subgroup $H$ of $G$. An extension of this result to the case of actions of compact Kac algebras on factors is also presented. No assumptions are made on the existence of a normal conditional expectation onto $N$.

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arXiv1996

Hilbert H*-modules and Hilbert modules over (non-self-adjoint) operator algebras -- a reference overview II

The two reference lists contain 54/22 references of papers and preprints concerned with the theory and/or various applications of Hilbert modules over Hilbert $*$-algebras and over (non-self-adjoint) operator algebras. They are far from being complete, but they give additional information about two research fields which are closely related to the theory of Hilbert C*-modules, i.e. they are complements to the reference guide about this circle of problems. Any additions, corrections and forthcoming information are welcome.

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arXiv1996

Super-connections and non-commutative geometry

We show that Quillen's formalism for computing the Chern character of the index using superconnections extends to arbitrary operators with functional calculus. We thus remove the condition that the operators have, up to homotopy, a gap in the spectrum. This is proved using differential graded algebras and non-commutative differential forms. Our results also give a new proof of the coincidence of the Chern character of a difference bundle defined using super-connections with the classical definition.

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arXiv1996

Covariant SPDEs and Quantum Field Structures

Covariant stochastic partial differential equations are studied in any dimension. A special class of such equations is selected and it is proven that the solutions can be analytically continued to Minkowski space-time yielding tempered Wightman distributions which are covariant, obey the locality axiom and a weak form of the spectral axiom. Key words: stochastic partial differential equations, white noise, covariant Markov generalized random fields, Euclidean QFT, Schwinger functions, Wightman distributions

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arXiv1996

Crossed Products by Dual Coactions of Groups and Homogeneous Spaces

Mansfield showed how to induce representations of crossed products of C*-algebras by coactions from crossed products by quotient groups and proved an imprimitivity theorem characterising these induced representations. We give an alternative construction of his bimodule in the case of dual coactions, based on the symmetric imprimitivity theorem of the third author; this provides a more workable way of inducing representations of crossed products of C*-algebras by dual coactions. The construction works for homogeneous spaces as well as quotient groups, and we prove an imprimitivity theorem for these induced representations.

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arXiv1996

Supermatrix Representations of Semigroup Bands

Various semigroups of noninvertible supermatrices of the special (antitriangle) shape having nilpotent Berezinian which appear in supersymmetric theories are defined and investigated. A subset of them continuously represents left and right zero semigroups and rectangular bands. The ideal properties of higher order rectangular band analogs and the ``wreath'' version of them are studied in detail. We introduce the ``fine'' equivalence relations leading to ``multidimesional'' eggbox diagrams. They are full images of Green's relations on corresponding subsemigroups.

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arXiv1996

Normal intermediate subfactors

Let $N \subset M$ be an irreducible inclusion of type type II$_1$ factors with finite Jones index. We shall introduce the notion of normality for intermediate subfactors of the inclusion $N \subset M$. If the depth of $N \subset M$ is 2, then an intermediate subfactor $K$ for $N \subset M$ is normal in $ N \subset M$ if and only if the depths of $N \subset K$ and $K \subset M$ are both 2. In particular, if $M$ is the crossed product $N \rtimes G$ of a finite group $G$, then $K = N \rtimes H$ is normal in $N \subset M$ if and only if $H$ is a normal subgroup of $G$.

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arXiv1996

Scaling algebras, the renormalization group and the principle of local stability in algebraic quantum field theory

We summarize the new scaling algebra approach to the structural analysis of the short distance behaviour of quantum field theories in the operator algebraic formulation which has recently been proposed by D. Buchholz, R. Verch (Rev. Math. Phys. 7(1995) 1195), and further studied by D. Buchholz (Ann. Inst. H. Poincare' 64(1996) 433, Nucl. Phys. B469(1996) 333). We also report on an extension of this framework to quantum field theory in curved spacetime.

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arXiv1996

Modules with norms which take values in a C*-algebra

We consider modules E over a C*-algebra A which are equipped with a map into A_+ that has the formal properties of a norm. We completely determine the structure of these modules. In particular, we show that if A has no nonzero commutative ideals then every such E must be a Hilbert module. The commutative case is much less rigid: if A = C_0(X) is commutative then E is merely isomorphic to the module of continuous sections of some bundle of Banach spaces over X. In general E will embed in a direct sum of modules of the preceding two types.

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