arXiv subjects

Vladimir Kapustin

Publications and source records attributed to Vladimir Kapustin.

3 recordsLinked to original sources

arXiv2017

On hypercyclic rank one perturbations of unitary operators

Recently, S. Grivaux showed that there exists a rank one perturbation of a unitary operator in a Hilbert space which is hypercyclic. Another construction was suggested later by the first and the third authors. Here, using a functional model for rank one perturbations of singular unitary operators, we give yet another construction of hypercyclic rank one perturbation of a unitary operator. In particular, we show that any Carleson set on the circle can be the spectrum of a perturbed (hypercyclic) operator.

math.FA↗

arXiv2015

Averaged wave operators and complex-symmetric operators

We study the behaviour of sequences $U_2^n X U_1^{-n}$, where $U_1, U_2$ are unitary operators, whose spectral measures are singular with respect to the Lebesgue measure, and the commutator $XU_1-U_2X$ is small in a sense. The conjecture about the weak averaged convergence of the difference $U_2^n X U_1^{-n}-U_2^{-n} X U_1^n$ to the zero operator is discussed and its connection with complex-symmetric operators is established in a general situation. For a model case where $U_1=U_2$ is the unitary operator of multiplication by $z$ on $L^2(μ)$, sufficient conditions for the convergence as in the Conjecture are given in terms of kernels of integral operators.

math.FA↗

arXiv2010

Symbols of truncated Toeplitz operators

We consider three problems connected with coinvariant subspaces of the backward shift operator in Hardy spaces $H^p$: 1) properties of truncated Toeplitz operators; 2) Carleson-type embedding theorems for the coinvariant subspaces; 3) factorizations of pseudocontinuable functions from $H^1$. These problems turn out to be closely connected and even, in a sense, equivalent. The new approach based on the factorizations allows us to answer a number of challenging questions about truncated Toeplitz operators posed by Donald Sarason.

math.FA↗