Abstract:
We consider the class $\Pi$ of contracting operators $T$ with spectrum on the unit
circle $\Gamma$, acting on a separable Hilbert space and subject to the following
restriction on the growth of the resolvent $R_T(\lambda)$:
$$
\sup_{0\leqslant\rho<1}\int^{2\pi}_0\ln^+\{(1-\rho)\|R_T(\rho e^{i\varphi})\|\}d\varphi<+\infty.
$$
We study the spectral subspaces $\Omega_T(B)$ for $T\in\Pi$, corresponding to arbitrary
Borel subsets of the circle $\Gamma$; in parallel we study a Borel measure $\omega_T(B)$ on $\Gamma$,
adequate for $\Omega_T(B)$ in the following sense:
$$
\Omega_T(B)=\{0\}\Longleftrightarrow\omega_T(B)=0.
$$