Operators with Diskcyclic Vectors Subspaces

Abstract

In this paper, we prove that if $T$ is diskcyclic operator then the closed unit disk multiplied by the union of the numerical range of all iterations of $T$ is dense in $\mathcal H$. Also, if $T$ is diskcyclic operator and $|\lambda|\le 1$, then $T-\lambda I$ has dense range. Moreover, we prove that if $\alpha >1$, then $\frac{1}{\alpha}T$ is hypercyclic in a separable Hilbert space $\mathcal H$ if and only if $T \oplus \alpha I_{\mathbb{C}}$ is diskcyclic in $\mathcal H \oplus \mathbb{C}$. We show at least in some cases a diskcyclic operator has an invariant, dense linear subspace or an infinite dimensional closed linear subspace, whose non-zero elements are diskcyclic vectors. However, we give some counterexamples to show that not always a diskcyclic operator has such a subspace.