On the regularity of Fourier interpolation formulas

Abstract: By applying new functional analysis tools in the framework of Fourier interpolation formulas, such as sc-Fredholm operators and Schauder frames, we are able to improve and refine several properties of these aforementioned formulas on the real line. As two examples of our main contributions, we highlight: (i) that we may upgrade perturbed interpolation bases all the way to the Schwartz space, which shows that even the perturbed interpolation formulas are as regular as the Radchenko-Viazovska case; (ii) that a certain subset of the interpolation formulae considered by Kulikov-Nazarov-Sodin may actually be upgraded to be convergent in the Schwartz class, giving a first partial answer to a question posed by those authors. As a final contribution of this work, we also show that, if the perturbations are sufficiently small, then even analyticity properties of the basis functions are preserved. This shows, in particular, that any function that vanishes on all but finitely many of the (perturbed) nodes is automatically analytic, a feature previously only known to hold in supercritical contexts besides the Radchenko-Viazovska case.