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Diagrammatics for the smallest quantum coideal and Jones–Wenzl projectors

Published online by Cambridge University Press:  22 April 2025

Catharina Stroppel*
Affiliation:
Department of Mathematics, University of Bonn, Bonn, Germany
Zbigniew Wojciechowski
Affiliation:
Department of Mathematics, University of Dresden, Dresden, Germany
*
Corresponding author: Catharina Stroppel; Email: [email protected]

Abstract

We describe algebraically, diagrammatically, and in terms of weight vectors, the restriction of tensor powers of the standard representation of quantum $\mathfrak {sl}_2$ to a coideal subalgebra. We realize the category as a module category over the monoidal category of type $\pm 1$ representations in terms of string diagrams and via generators and relations. The idempotents projecting onto the quantized eigenspaces are described as type $B/D$ analogues of Jones–Wenzl projectors. As an application, we introduce and give recursive formulas for analogues of $\Theta$-networks.

Type
Research Article
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of Glasgow Mathematical Journal Trust

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