# Journal of Operator Theory

Volume 88, Issue 2, Fall 2022  pp. 275-288.

Trace formula for contractions and its representation in $\mathbb{D}$

Authors:  Arup Chattopadhyay (1), Kalyan B. Sinha (2)
Author institution:(1) Department of Mathematics, Indian Institute of Technology Guwahati, Guwahati, 781039, India
(2) Theoretical Sciences Unit, Jawaharlal Nahru Centre For Advanced Scientific Research, Bangalore, 560064, India

Summary: The aim of this article is twofold: give a short proof of the existence of real spectral shift function and the associated trace formula for a pair of contractions, the difference of which is trace-class and one of the two a strict contraction, so that the set of assumptions is minimal in comparison to those in all the existing proofs. The second one is to find a trace formula for differences of functions of a contraction and its adjoint, in which case, the integral in the formula is over the unit disc and has an expression surprisingly similar to the Helton--Howe formula.

DOI: http://dx.doi.org/10.7900/jot.2021may13.2323
Keywords: Kre\u \i n's trace formula, spectral shift function, self adjoint operators, unitary operators, contractions, unitary dilations