Functions of self-adjoint operators in ideals of compact operators

TL;DR

This paper establishes bounds for differences of functions of self-adjoint operators within ideals of compact operators, especially for functions with finitely many non-smooth points, and applies these to Wiener-Hopf operators.

Contribution

It provides new bounds for operator differences involving functions with limited smoothness and applies them to asymptotic trace formulas for Wiener-Hopf operators.

Findings

Derived bounds for $f(A)J - Jf(B)$ in quasi-normed ideals.

Applied results to obtain asymptotic trace formulas for Wiener-Hopf operators.

Analyzed functions with finitely many non-smooth points, like $|t|^eta$.

Abstract

For self-adjoint operators $A, B$, a bounded operator $J$, and a function $f:\mathbb R\to\mathbb C$ we obtain bounds in quasi-normed ideals of compact operators for the difference $f(A)J-Jf(B)$ in terms of the operator $AJ-JB$. The focus is on functions $f$ that are smooth everywhere except for finitely many points. A typical example is the function $f(t) = |t|^\gamma$ with $\gamma \in (0, 1)$. The obtained results are applied to derive a two-term quasi-classical asymptotic formula for the trace $tr f(S)$ with $S$ being a Wiener-Hopf operator with a discontinuous symbol.