Property (T) and exotic quantum group norms

TL;DR

This paper uses property (T) to construct new quantum group norms, generalizes classical property (T) characterizations to quantum groups, and addresses open problems in quantum group theory.

Contribution

It introduces new quantum group norms based on property (T) and extends classical operator algebraic characterizations to the quantum setting.

Findings

Constructed new quantum group norms that differ from minimal and maximal norms.

Generalized classical property (T) characterizations to quantum groups.

Provided tools to solve open problems on automatic continuity and coproduct structure.

Abstract

Utilizing the notion of property (T) we construct new examples of quantum group norms on the polynomial algebra of a compact quantum group, and provide criteria ensuring that these are not equal to neither the minimal nor the maximal norm. Along the way we generalize several classical operator algebraic characterizations of property (T) to the quantum group setting which unify recent approaches to property (T) for quantum groups with previous ones. The techniques developed furthermore provide tools to answer two open problems; firstly a question by B\'edos, Murphy and Tuset about automatic continuity of the comultiplication and secondly a problem left open by Woronowicz regarding the structure of elements whose coproduct is a finite sum of simple tensors.