Frames of orbits of multiplication operators on Hardy spaces

Abstract

We study frames for Hardy spaces generated by orbits of multiplication operators. We characterize the symbols $φ\in H^\infty(\mathbb{T}^N)$ for which the multiplication operator $M_φ$ admits a frame of orbits on $H^2(\mathbb{T}^N)$. We also show that, in this setting, the existence of a frame is equivalent to the existence of a Parseval frame. Moreover, for $N=1$ we prove that finitely many orbits suffice if and only if $φ$ is a finite Blaschke product. For $N > 1$, no finite collection of orbits can generate a frame, regardless of the symbol. We study the analogous problem for the adjoint operator $M_φ^*$. Our results extend to the infinite-dimensional torus $\mathbb{T}^\infty$ and, via Bohr's transform, to the Hardy space of Dirichlet series $\mathcal{H}_2$.