arXiv subjects

Leonard Huang

Publications and source records attributed to Leonard Huang.

8 recordsLinked to original sources

arXiv2023

The Covariant Stone-von Neumann Theorem for Locally Compact Quantum Groups

The Stone-von Neumann Theorem is a fundamental result which unified the competing quantum mechanical models of matrix mechanics and wave mechanics. It's mechanism of proof ultimately involved the study of unitary group representations on a Hilbert space. In this article, we continue the broad generalization set out in arxiv:1903.09351 and arxiv:2109.08997, analyzing representations of locally compact quantum dynamical systems defined on Hilbert modules, of which the classical result is a special case. We introduce a pair of modular representations which subsume numerous models which appear in the literature, and for certain coactions (G, A, {\alpha}) recover the multiplicity results of arxiv:2109.08997. As a corollary, we develop a new criterion for identifying strongly regular locally compact quantum groups, related to the study of their dynamics on elementary C*-algebras.

math.OA↗

arXiv2022

Group Actions on Product Systems

We introduce the concept of crossed product of a product system by a locally compact group. We prove that the crossed product of a row-finite and faithful product system by an amenable group is also a row-finite and faithful product system. We illustrate with examples related to group actions on $k$-graphs and to higher rank Doplicher-Roberts algebras.

math.OA↗

arXiv2022

The Modular Stone-von Neumann Theorem

In this paper, we use the tools of nonabelian duality to formulate and prove a far-reaching generalization of the Stone-von Neumann Theorem to modular representations of actions and coactions of locally compact groups on elementary $ C^{\ast} $-algebras. This greatly extends the Covariant Stone-von Neumann Theorem for Actions of Abelian Groups recently proven by L. Ismert and the second author. Our approach is based on a new result about Hilbert $ C^{\ast} $-modules that is simple to state yet is widely applicable and can be used to streamline many previous arguments, so it represents an improvement -- in terms of both efficiency and generality -- in a long line of results in this area of mathematical physics that goes back to J. von Neumann's proof of the classical Stone-von Neumann Theorem.

math.OA↗

arXiv2021

Cocycles on Certain Groupoids Associated to $ \mathbb{N}^{k} $-Actions

We consider groupoids constructed from a finite number of commuting local homeomorphisms acting on a compact metric space, and study generalized Ruelle operators and $ C^{\ast} $-algebras associated to these groupoids. We provide a new characterization of $ 1 $-cocycles on these groupoids taking values in a locally compact abelian group, given in terms of $ k $-tuples of continuous functions on the unit space satisfying certain canonical identities. Using this, we develop an extended Ruelle-Perron-Frobenius theory for dynamical systems of several commuting operators ($ k $-Ruelle triples and commuting Ruelle operators). Results on KMS states on $ C^{\ast} $-algebras constructed from these groupoids are derived. When the groupoids being studied come from higher-rank graphs, our results recover existence-uniqueness results for KMS states associated to the graphs.

math.OA↗

arXiv2019

The Covariant Stone-von Neumann Theorem for Actions of Abelian Groups on $ C^{\ast} $-Algebras of Compact Operators

In this paper, we formulate and prove a version of the Stone-von Neumann Theorem for every $ C^{\ast} $-dynamical system of the form $ (G,\mathbb{K}(\mathcal{H}),α) $, where $ G $ is a locally compact Hausdorff abelian group and $ \mathcal{H} $ is a Hilbert space. The novelty of our work stems from our representation of the Weyl Commutation Relation on Hilbert $ \mathbb{K}(\mathcal{H}) $-modules instead of just Hilbert spaces, and our introduction of two additional commutation relations, which are necessary to obtain a uniqueness theorem. Along the way, we apply one of our basic results on Hilbert $ C^{\ast} $-modules to significantly shorten the length of Iain Raeburn's well-known proof of Takai-Takesaki Duality.

math-ph↗

arXiv2018

Metrized Quantum Vector Bundles over Quantum Tori Built from Riemannian Metrics and Rosenberg's Levi-Civita Connections

We build metrized quantum vector bundles, over a generically transcendental quantum torus, from Riemannian metrics, using Rosenberg's Levi-Civita connections for these metrics. We also prove that two metrized quantum vector bundles, corresponding to positive scalar multiples of a Riemannian metric, have distance zero between them with respect to the modular Gromov-Hausdorff propinquity.

math.OA↗

arXiv2017

Generalized Fixed-Point Algebras for Twisted $ C^{\ast} $-Dynamical Systems

In his seminal paper "Generalized Fixed Point Algebras and Square-Integrable Group Actions", Ralf Meyer showed how to construct generalized fixed-point algebras for $ C^{\ast} $-dynamical systems via their square-integrable representations on Hilbert $ C^{\ast} $-modules. His method extends Marc Rieffel's construction of generalized fixed-point algebras from proper group actions on $ C^{\ast} $-algebras. This dissertation seeks to generalize Meyer's work to construct generalized fixed-point algebras for twisted $ C^{\ast} $-dynamical systems. To accomplish this, we must introduce some new concepts, the foremost being that of a twisted Hilbert $ C^{\ast} $-module, which is a Hilbert $ C^{\ast} $-module equipped with a twisted group action by bijective linear isometries that is compatible with the module's right $ C^{\ast} $-algebra action and its $ C^{\ast} $-algebra-valued inner product. Twisted Hilbert $ C^{\ast} $-modules over a fixed twisted $ C^{\ast} $-dynamical system form a category, where morphisms are twisted-equivariant adjointable operators. Given a twisted $ C^{\ast} $-dynamical system, we provide a definition of a relatively continuous subspace of a twisted Hilbert $ C^{\ast} $-module (inspired by an idea due to Ruy Exel), and then prescribe a method of constructing, from such a subspace, a generalized fixed-point algebra that is Morita-Rieffel equivalent to an ideal of the corresponding reduced twisted crossed product. Our construction thus generalizes that of Meyer and, by extension, that of Rieffel. Our main result is the description of a classifying category for the class of all Hilbert modules over a reduced twisted crossed product. This implies that every Hilbert module over a $ d $-dimensional non-commutative torus can be constructed from a Hilbert space endowed with a twisted $ \mathbb{Z}^{d} $-action by unitary operators and a relatively continuous subspace.

math.RT↗

arXiv2017

An Infinitesimal Version of the Stone-von Neumann Theorem

In this paper, we present an infinitesimal version of the Stone-von Neumann Theorem. This work was motivated by the need to formulate the uniqueness property of the Heisenberg Commutation Relation purely in terms of unbounded operators.

math-ph↗