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arXiv · 2401.15591

Complete Nevanlinna-Pick Kernels and the Curvature Invariant

Tirthankar Bhattacharyya·Abhay Jindal
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Abstract

We consider a unitarily invariant complete Nevanlinna-Pick kernel denoted by $s$ and a commuting $d$-tuple of bounded operators $T = (T_{1}, \dots, T_{d})$ satisfying a natural contractivity condition with respect to $s$. We associate with $T$ its curvature invariant which is a non-negative real number bounded above by the dimension of a defect space of $\bfT$. The instrument which makes this possible is the characteristic function developed in \cite{BJ}. \medskip We present an asymptotic formula for the curvature invariant. In the special case when $\bfT$ is pure, we provide a notably simpler formula, revealing that in this instance, the curvature invariant is an integer. We further investigate its connection with an algebraic invariant known as fibre dimension. Moreover, we obtain a refined and simplified asymptotic formula for the curvature invariant of $\bfT$ specifically when its characteristic function is a polynomial.

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Tirthankar Bhattacharyya, Abhay Jindal. 2024-01-28. Complete Nevanlinna-Pick Kernels and the Curvature Invariant. https://arxiv.org/abs/2401.15591

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