The truncated matrix trigonometric moment problem with an open gap

Abstract

This paper is a continuation of our previous investigations on the truncated matrix trigonometric moment problem in Ukrainian Math. J., 2011, \textbf{63}, no. 6, 786-797, and Ukrainian Math. J., 2013, \textbf{64}, no. 8, 1199-1214. In this paper we shall study the truncated matrix trigonometric moment problem with an additional constraint posed on the matrix measure $M_{\mathbb{T}}(\delta)$, $\delta\in \mathfrak{B}(\mathbb{T})$, generated by the seeked function $M(x)$: $M_{\mathbb{T}}(\Delta) = 0$, where $\Delta$ is a given open subset of $\mathbb{T}$ (called a gap). We present necessary and sufficient conditions for the solvability of the moment problem with a gap. All solutions of the moment problem with a gap can be constructed by a Nevanlinna-type formula.