Linear differential equations with slowly growing solutions

This research concerns coefficient conditions for linear differential equations in the unit disc of the complex plane. In the higher order case the separation of zeros (of maximal multiplicity) of solutions is considered, while in the second order case slowly growing solutions in $H^{\mathrm{\infty }}$, $\mathrm{B}\mathrm{M}\mathrm{O}\mathrm{A}$ and the Bloch space are discussed. A counterpart of the Hardy-Stein-Spencer formula for higher derivatives is proved, and then applied to study solutions in the Hardy spaces.