arXiv subjects

Upasana Kashyap

Publications and source records attributed to Upasana Kashyap.

4 recordsLinked to original sources

arXiv2017

Rigged modules I: modules over dual operator algebras and the Picard group

In a previous paper we generalized the theory of W*-modules to the setting of modules over nonselfadjoint dual operator algebras, obtaining the class of weak*-rigged modules. At that time we promised a forthcoming paper devoted to other aspects of the theory. We fulfill this promise in the present work and its sequel "Rigged modules II", giving many new results about weak*-rigged modules and their tensor products. We also discuss the Picard group of weak* closed subalgebras of a commutative algebra. For example, we compute the weak Picard group of $H^{\infty}(D)$, and prove that for a weak* closed function algebra A, the weak Picard group of A is a semidirect product of the automorphism group of A, and the subgroup consisting of symmetric equivalence bimodules.

math.OA↗

arXiv2009

A characterization and a generalization of W*-modules

We give a new Banach module characterization of $W^*$-modules, also known as selfdual Hilbert $C^*$-modules over a von Neumann algebra. This leads to a generalization of the notion, and the theory, of W*-modules, to the setting where the operator algebras are $σ$-weakly closed algebras of operators on a Hilbert space. That is, we find the appropriate weak* topology variant of our earlier notion of {\em rigged modules}, and their theory, which in turn generalizes the notions of C*-module, and Hilbert space, successively. Our {\em w*-rigged modules} have canonical `envelopes' which are W*-modules. Indeed, w*-rigged modules may be defined to be a subspace of a W*-module possessing certain properties.

math.OA↗

arXiv2008

A Morita theorem for dual operator algebras

We prove that two dual operator algebras are weak$^*$ Morita equivalent if and only if they have equivalent categories of dual operator modules via completely contractive functors which are also weak$^*$-continuous on appropriate morphism spaces. Moreover, in a fashion similar to the operator algebra case, we characterize such functors as the module normal Haagerup tensor product with an appropriate weak$^*$ Morita equivalence bimodule. We also develop the theory of the $W^*$-dilation, which connects the non-selfadjoint dual operator algebra with the $W^*$-algebraic framework. In the case of weak$^*$ Morita equivalence, this $W^*$-dilation is a $W^*$-module over a von Neumann algebra generated by the non-selfadjoint dual operator algebra. The theory of the $W^*$-dilation is a key part of the proof of our main theorem.

math.OA↗

arXiv2007

Morita equivalence of dual operator algebras

We consider a variant of the notion of Morita equivalence appropriate to weak* closed algebras of Hilbert space operators, which we call {\em weak Morita equivalence}. We obtain new variants, appropriate to the dual algebra setting, of the basic theory of strong Morita equivalence, and new nonselfadjoint variants of aspects of Rieffel's $W^*$-algebraic Morita equivalence.

math.OA↗