Second order trace formulae

TL;DR

This paper provides new proofs and extensions of the Koplienko trace formula for pairs of contractions, self-adjoint, and dissipative operators, using finite-dimensional reduction, dilation techniques, and Cayley transforms.

Contribution

It introduces a new proof of the Koplienko trace formula for contractions with a normal initial operator and extends the formula to various operator classes.

Findings

Proof of Koplienko trace formula for contractions with normal initial operator

Extension of the formula to pairs of self-adjoint and dissipative operators

Application of dilation and Cayley transform techniques

Abstract

Koplienko \cite{Ko} found a trace formula for perturbations of self-adjoint operators by operators of Hilbert-Schmidt class $\mathcal{B}_2(\mathcal{H})$. Later, Neidhardt introduced a similar formula in the case of pair of unitaries $(U,U_0)$ via multiplicative path in \cite{NH}. In 2012, Potapov and Sukochev \cite{PoSu} obtained a trace formula like the Koplienko trace formula for pairs of contractions by answering an open question posed by Gesztesy, Pushnitski, and Simon in \cite[Open Question 11.2]{GePu}. In this article, we supply a new proof of the Koplienko trace formula in the case of pair of contractions $(T,T_0)$, where the initial operator $T_0$ is normal, via linear path by reducing the problem to a finite-dimensional one as in the proof of Krein's trace formula by Voiculescu \cite{Voi}, Sinha and Mohapatra \cite{MoSi94,MoSi96}. Consequently, we obtain the Koplienko trace formula for a class of pairs of contractions using the Sch\"{a}ffer matrix unitary dilation. Moreover, we also obtain the Koplienko trace formula for a pair of self-adjoint operators and maximal dissipative operators using the Cayley transform. At the end, we extend the Koplienko-Neidhardt trace formula for a class of pair of contractions $(T,T_0)$ via multiplicative path.