Between the von Neumann inequality and the Crouzeix conjecture

Patryk Pagacz, Paweł Pietrzycki, Michał Wojtylak

A new concept of a deformed numerical range $W^{\rho }(T)$ is introduced. Here $T$ is a bounded linear operator or a matrix and $\rho \in [1,+\infty )$ is a parameter. Each $W^{\rho }(T)$ is a clos…