Searcharxiv⌕ Search

arXiv subjects

Johan Kustermans

Publications and source records attributed to Johan Kustermans.

15 recordsLinked to original sources
arXiv2010

The dual quantum group for the quantum group analogue of the normalizer of SU(1,1) in SL(2,C)

The quantum group analogue of the normalizer of SU(1,1) in SL(2,C) is an important and non-trivial example of a non-compact quantum group. The general theory of locally compact quantum groups in the operator algebra setting implies the existence of the dual quantum group. The first main goal of the paper is to give an explicit description of the dual quantum group for this example involving the quantized enveloping algebra U_q(su(1,1)). It turns out that U_q(su(1,1)) does not suffice to generate the dual quantum group. The dual quantum group is graded with respect to commutation and anticommutation with a suitable analogue of the Casimir operator characterized by an affiliation relation to a von Neumann algebra. This is used to obtain an explicit set of generators. Having the dual quantum group the left regular corepresentation of the quantum group analogue of the normalizer of SU(1,1) in SL(2,C) is decomposed into irreducible corepresentations. Upon restricting the irreducible corepresentations to U_q(su(1,1))-representation one finds combinations of the positive and negative discrete series representations with the strange series representations as well as combinations of the principal unitary series representations. The detailed analysis of this example involves analysis of special functions of basic hypergeometric type and, in particular, some results on these special functions are obtained, which are stated separately. The paper is split into two parts; the first part gives almost all of the statements and the results, and the statements in the first part are independent of the second part. The second part contains the proofs of all the statements.

math.QA↗
arXiv2001

A locally compact quantum group analogue of the normalizer of SU(1,1) in SL(2,C)

S.L. Woronowicz proved in 1991 that quantum SU(1,1) does not exist as a locally compact quantum group. Results by L.I. Korogodsky in 1994 and more recently by Woronowicz gave strong indications that the normalizer N of SU(1,1) in SL(2,C) is a much better quantization candidate than SU(1,1) itself. In this paper we show that this is indeed the case by constructing N_q, a new example of a unimodular locally compact quantum group (depending on a parameter q) that is a deformation of N. After defining the underlying von Neumann algebra of N_q we use a certain class of q-hypergeometric functions and their orthogonality relations to construct the comultiplication. The coassociativity of this comultiplication is the hardest result to establish. We define the Haar weight and obtain simple formulas for the antipode and its polar decomposition. As a final result we produce the underlying C*-algebra of N_q. The proofs of all these results depend on various properties of q-hypergeometric 1\phi1 functions.

math.QA↗
arXiv2000

Induced corepresentations of locally compact quantum groups

We introduce the construction of induced corepresentations in the setting of locally compact quantum groups and prove that the resulting induced corepresentations are unitary under some mild integrability condition. We also establish a quantum analogue of the classical bijective correspondence between quasi-invariant measures and certain measures on the larger locally compact group.

math.OA↗
arXiv2000

Locally compact quantum groups in the von Neumann algebraic setting

In this paper we complete in several aspects the picture of locally compact quantum groups. First of all we give a definition of a locally compact quantum group in the von Neumann algebraic setting and show how to deduce from it a C*-algebraic quantum group. Further we prove several results about locally compact quantum groups which are important for applications, but were not yet settled in our paper "Locally compact quantum groups". We prove a serious strengthening of the left invariance of the Haar weight, and we give several formulas connecting the locally compact quantum group with its dual. Loosely speaking we show how the antipode of the locally compact quantum group determines the modular group and modular conjugation of the dual locally compact quantum group.

math.OA↗
arXiv1999

Locally compact quantum groups in the universal setting

In this paper we associate to every reduced C*-algebraic quantum group A a universal C*-algebraic quantum group. We fine tune a proof of Kirchberg to show that every *-representation of a modified L1-space is generated by a unitary corepresentation. By taking the universal enveloping C*-algebra of a dense sub *-algebra of A we arrive at the uinversal C*-algebra. We show that this universal C*-algebra carries a quantum group structure which is as rich as its reduced companion.

math.OA↗
arXiv1999

Weight theory for C*-algebraic quantum groups

In this paper, we collect some technical results about weights on C*-algebras which are useful in de theory of locally compact quantum groups in the C*-algebra framework. We discuss the extension of a lower semi-continuous weight to a normal weight following S. Baaj, look into slice weights and their KSGNS-constructions and investigate the tensor product of weights together with a partial GNS-construction for such a tensor product. This paper accompanies our paper 'Locally compact quantum groups' in which we propose a relatively simple definition of a locally compact quantum group in the C*-algebra framework.

math.OA↗
arXiv1997

One-parameter representations on C*-algebras

Strongly continuous one-parameter representations on C*-algebras and their extension to the multiplier algebra are investigated. We give also a proof of the Stone theorem on Hilbert C*-modules and look into some related problems.

funct-an↗
arXiv1997

The analytic structure of an algebraic quantum group

A. Van Daele introduced and investigated so-called algebraic quantum groups. We proved that such algebraic quantum groups give rise to C*-algebraic quantum groups in the sense of Masuda, Nakagami & Woronowicz. We prove in this paper that the analytic structure of these C*-algebraic quantum groups can be pulled down to the algebraic quantum group.

funct-an↗
arXiv1997

KMS-weights on C*-algebras

In this paper, we build a solid framework for KMS-weights on C*-algebras. We use another definition than the one introduced by Combes, but prove that they are equivalent.

funct-an↗
arXiv1997

Universal C*-algebraic quantum groups arising from algebraic quantum groups

In this paper, we construct a universal C*-algebraic quantum group out of an algebraic one. We show that this universal C*-algebraic quantum group has the same rich structure as its reduced companion. This universal C*-algebraic quantum group also satifies an upcoming definition of Masuda, Nakagami & Woronowicz except for the possible non-faithfulness of the left Haar weight.

funct-an↗
arXiv1997

Examining the dual of an algebraic quantum group

In the first part of this paper, we implement the multiplier algebra of the dual of an algebraic quantum group (A,Delta) as a space of linear functionals on A. In the second part, we construct the universal corepresentation of (A,Delta) and use it to prove a bijective correspondence between corepresentations of (A,Delta) and homomorphisms on the dual.

funct-an↗
arXiv1997

A natural extension of a left invariant lower semi-continuous weight

In this paper, we describe a natural method to extend left invariant weights on C*-algebraic quantum groups. This method is then used to improve the left invariance property of a left invariant weight. We also prove some kind of uniqueness result for left Haar weights on C*-algebraic quantum groups arising from algebraic ones.

funct-an↗
arXiv1997

Regular C*-valued weights

We introduce the notion of a C*-valued weight between two C*-algebras as a generalization of an ordinary weight on a C*-algebra and as a C*-version of operator valued weights on von Neumann algebras. Also, some form of lower semi-continuity will be discussed together with an extension to the multiplier algebra. A strong but useful condition for C*-valued weights, the so-called regularity, is introduced. At the same time, we propose a construction procedure for such regular C*-valued weights. This construction procedure will be used to define the tensor product of regular C*-valued weights.

funct-an↗