7 papers
A Duflo-Moore theorem for ergodic group actions on semifinite von Neumann algebras
Ulrik Enstad, Hannes Wendt
We prove a generalization of the orthogonality relations of Duflo and Moore for ergodic, trace-preserving group actions on von Neumann algebras that are integrable in a suitable se…
Z-stability of twisted group C*-algebras of nilpotent groups
Ulrik Enstad, Eduard Vilalta
We prove that the twisted group C*-algebra of a finitely generated nilpotent group is -stable if and only if it is nowhere scattered, a condition that we characterize…
On the Calderón sum formula for wavelet systems
Ulrik Enstad, Jordy Timo van Velthoven
We show that the Calderón sum formula for orthonormal wavelet bases holds for arbitrary dilation and translation matrices under a mild condition on the wavelet function. This part…
Exponential frames and Riesz sequences at the critical density
Ulrik Enstad, Jordy Timo van Velthoven
We characterize exponential systems on sets of finite measure that form a frame or a Riesz sequence at the critical density. Namely, they are precisely those systems for which the…
Bessel duality of Gabor systems: A von Neumann algebraic perspective
Ulrik Enstad, Franz Luef
Bessel duality of regular Gabor systems states that a Gabor system over a lattice is a Bessel sequence if and only if the corresponding Gabor system over the adjoint lattice is a B…
Linear independence of coherent systems associated to discrete subgroups
Ulrik Enstad, Jordy Timo van Velthoven
This note considers the finite linear independence of coherent systems associated to discrete subgroups. We show by simple arguments that such coherent systems of amenable groups a…