Cyclicity of the shift operator and a related completeness problem in de Branges-Rovnyak spaces

In this paper, we study the cyclic vectors of the shift operator $S_b$ acting on de Branges-Rovnyak space $\mathcal{H}(b)$ associated to a non-extreme point of the closed unit ball of $H^{\mathrm{\infty }}$. We highlight an interesting link with a completeness problem that we study using the Cauchy transform. This enables us to obtain some nice consequences on cyclicity.