Norm resolvent convergence of discretized Fourier multipliers

TL;DR

This paper establishes explicit norm resolvent convergence estimates for discretized Fourier multiplier operators, including fractional Laplacians, with implications for spectral approximation accuracy.

Contribution

It provides the first explicit norm estimates for the resolvent differences between continuous operators and their discretizations, including spectral convergence rates.

Findings

Norm estimates depend explicitly on mesh size.

Spectral distances decay at the same rate as resolvent estimates.

Results apply to operators like fractional Laplacian and pseudo-relativistic Hamiltonian.

Abstract

We prove norm estimates for the difference of resolvents of operators and their discrete counterparts, embedded into the continuum using biorthogonal Riesz sequences. The estimates are given in the operator norm for operators on square integrable functions, and depend explicitly on the mesh size for the discrete operators. The operators are a sum of a Fourier multiplier and a multiplicative potential. The Fourier multipliers include the fractional Laplacian and the pseudo-relativistic free Hamiltonian. The potentials are real, bounded, and H\"older continuous. As a side-product, the Hausdorff distance between the spectra of the resolvents of the continuous and discrete operators decays with the same rate in the mesh size as for the norm resolvent estimates. The same result holds for the spectra of the original operators in a local Hausdorff distance.