Higher-derivative harmonic oscillators: stability of classical dynamics and adiabatic invariants Nicolas Boulanger, Fabien Buisseret, Frédéric Dierick and Olivier White Eur. Phys. J. C, 79 1 (2019) 60 Published online: 28 January 2019 DOI: 10.1140/epjc/s10052-019-6569-y