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Published online by Cambridge University Press: 18 July 2025
We study density properties of orbits for a hypercyclic operator T on a separable Banach space X, and show that exactly one of the following four cases holds: (1) every vector in X is asymptotic to zero with density one; (2) generic vectors in X are distributionally irregular of type $1$; (3) generic vectors in X are distributionally irregular of type
$2\frac {1}{2}$ and no hypercyclic vector is distributionally irregular of type
$1$; (4) every hypercyclic vector in X is divergent to infinity with density one. We also present some examples concerned with weighted backward shifts on
$\ell ^p$ to show that all the above four cases can occur. Furthermore, we show that similar results hold for
$C_0$-semigroups.
J. Li was supported in part by NSF of China (12222110). X. Wang was partially supported by STU Scientific Research Initiation Grant (SRIG, No. NTF22020) and NSF of China (12301230). J. Zhao was supported by NSF of China (12301226).