Abstract:
Let $B$ be a completely nonselfadjoint dissipative Volterra operator acting in a separable Hilbert space $\mathfrak Y$ whose resolvent $(I-\lambda B)^{-1}$ has finite exponential type. Further, let $\mathfrak{L}=(B-B^*)\mathfrak Y$, $y\in\mathfrak{L}$, and
$y(\lambda)=(I-\lambda B)^{-1}y$. In this article conditions are determined on the operator $B$, the vector $y$, and the sequence $\Lambda=\{\lambda_k\}_{-\infty}^{+\infty}$ under which the family
$$
\{y(\lambda_k):\lambda_k\in \Lambda\}, \qquad
\inf_{\lambda_k}\operatorname{Im}\lambda_k>0,
$$
forms an unconditional basis in the space $\mathfrak Y$. Moreover, a new approach is considered for the problem of similarity of dissipative Volterra operators, based on a study of the basis properties of this system of vectors.
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