On the set of hypercyclic vectors for the differentiation operator

TL;DR

This paper proves that the set of hypercyclic vectors for the differentiation operator on entire functions contains a non-trivial subalgebra and an infinite dimensional closed linear subspace, answering longstanding questions.

Contribution

It establishes the existence of a non-trivial subalgebra and an infinite dimensional closed linear subspace within the hypercyclic vectors for the differentiation operator.

Findings

The set of hypercyclic vectors contains a non-trivial subalgebra.

The set of hypercyclic vectors contains an infinite dimensional closed linear subspace.

Both questions raised by Aron, Conejero, Peris, and Seoane-Sepúlveda are affirmatively answered.

Abstract

Let $D$ be the differentiation operator $Df=f'$ acting on the Fr\'echet space $\H$ of all entire functions in one variable with the standard (compact-open) topology. It is known since 1950's that the set $H(D)$ of hypercyclic vectors for the operator $D$ is non-empty. We treat two questions raised by Aron, Conejero, Peris and Seoane-Sep\'ulveda whether the set $H(D)$ contains (up to the zero function) a non-trivial subalgebra of $\H$ or an infinite dimensional closed linear subspace of $\H$. In the present article both questions are answered affirmatively.