A Besov class functional calculus for bounded holomorphic semigroups

It is well-known that -sectorial operators generally do not admit a bounded H^∞ calculus over the right half-plane. In contrast to this, we prove that the H^∞ calculus is bounded over any class of functions whose Fourier spectrum is contained in some interval [ε,σ] with 0<ε<σ<∞. The constant bounding this calculus grows as as and this growth is sharp over all Banach space operators of the class under consideration. It follows from these estimates that -sectorial operators admit a bounded calculus over the Besov algebra of the right half-plane. We also discuss the link between -sectorial operators and bounded Tadmor-Ritt operators.     

Generalized functional calculus in lattice-ordered algebras

We construct a functional calculus on unital uniformly complete f-algebras for continuous center-valued functions of polynomial growth and study the connection with the Minkowski duality.     

The Hille-Yosida theorem for resolvent operators of multiparameter semigroups

We consider multiparameter semigroups of two types (multiplicative and coordinatewise) and resolvent operators associated with such semigroups. We prove an alternative version of the Hille-Yosida theorem in terms of resolvent operators. For simplicity of presentation, we give statements and proofs for two-parameter semigroups.     

Functional calculus for generators of uniformly bounded holomorphic semigroups

We present a method for constructing a functional calculus for (possibly unbounded) operators that generate a uniformly bounded holomorphic semigroup, e^−zA. (A will be called a generator.) These are closed, densely defined operators whose spectrum and numerical range are contained in [0,∞), with respect to an equivalent norm.     

Generalized Mehler semigroups and applications

Summary We construct and study generalized Mehler semigroups (p _t ) _t 0 and their associated Markov processesM. The construction methods for (p _t ) _t 0 are based on some new purely functional analytic results implying, in particular, that any strongly continuous semigroup on a Hilbert spaceH can be extended to some larger Hilbert spaceE, with the embeddingHE being Hilbert-Schmidt. The same analytic extension results are applied to construct strong solutions to stochastic differential equations of typedX _t =C dW _t +AX _t dt (with possibly unbounded linear operatorsA andC onH) on a suitably chosen larger spaceE. For Gaussian generalized Mehler semigroups (p _t ) _t 0 with corresponding Markov processM, the associated (non-symmetric) Dirichlet forms (E D(E)) are explicitly calculated and a necessary and sufficient condition for path regularity ofM in terms of (E,D(E)) is proved. Then, using Dirichlet form methods it is shown thatM weakly solves the above stochastic differential equation if the state spaceE is chosen appropriately. Finally, we discuss the differences between these two methods yielding strong resp. weak solutions.     

Generalized Cayley graphs of semigroups I

We introduce the concept of generalized Cayley graphs of semigroups and discuss their fundamental properties, and then study a special case, the universal Cayley graphs of semigroups so that some general results are given and the universal Cayley graph of a -partial order of complete graphs with loops is described.     

Generalized Cayley graphs of semigroups II

Following Zhu (Semigroup Forum, 2011, doi:), we study generalized Cayley graphs of semigroups. The Cayley D-saturated property, a particular combinatorial property, of generalized Cayley graphs of semigroups is considered and most of the results in Kelarev and Quinn (Semigroup Forum 66:89–96, 2003), Yang and Gao (Semigroup Forum 80:174–180, 2010) are extended. In addition, for some basic graphs and their complete fission graphs, we describe all semigroups whose universal Cayley graphs are isomorphic to these graphs.     

A local functional calculus

This paper introduces a local functional calculus for a class of bounded operators on a Hilbert space. Properties of the local functional calculus are investigated and an application is given to subnormal operators. Also, the concept of a locally rationally multicyclic operator is introduced and the Berger-Shaw Theorem is discussed.During the preparation of this paper the author was partially supported by National Science Foundation grant MCS 83-20426.     

A new functional calculus for noncommuting operators

In this paper we use the notion of slice monogenic functions [F. Colombo, I. Sabadini, D.C. Struppa, Slice monogenic functions, Israel J. Math., in press] to define a new functional calculus for an n-tuple T of not necessarily commuting operators. This calculus is different from the one discussed in [B. Jefferies, Spectral Properties of Noncommuting Operators, Lecture Notes in Math., vol. 1843, Springer-Verlag, Berlin, 2004] and it allows the explicit construction of the eigenvalue equation for the n-tuple T based on a new notion of spectrum for T. Our functional calculus is consistent with the Riesz-Dunford calculus in the case of a single operator.     

Bicomplex holomorphic functional calculus

In this paper we introduce and study a functional calculus for bicomplex linear bounded operators. The study is based on the decomposition of bicomplex numbers and of linear operators using the two nonreal idempotents. We show that, due to the presence of zero divisors in the bicomplex numbers, the spectrum of a bounded operator is unbounded. We therefore introduce a different spectrum (called reduced spectrum) which is bounded and turns out to be the right tool to construct the bicomplex holomorphic functional calculus. Finally we provide some properties of the calculus.     

Generalized state machines and generalized transformation semigroups

We introduce the concepts of a generalized state machine and a generalized transformation semigroup and discuss their algebraic properties.     

A Wiener-Young type theorem for dual semigroups

The purpose of this paper is to obtain extensions of the Wiener-Young theorem for strongly continuous semigroups of positive operators in Banach lattices.     

Finite derivation type for semilattices of semigroups

In this paper we investigate how the combinatorial property finite derivation type (FDT) is preserved in a semilattice of semigroups. We prove that if $S= \mathcal{S}[Y,S_{\alpha}]$ is a semilattice of semigroups such that Y is finite and each S _?? (????Y) has FDT, then S has FDT. As a consequence we can show that a strong semilattice of semigroups $\mathcal{S}[Y,S_{\alpha},\lambda_{\alpha,\beta}]$ has FDT if and only if Y is finite and every semigroup S _?? (????Y) has FDT.