Casimir effect in quadratic theories of gravity Luca Buoninfante, Gaetano Lambiase, Luciano Petruzziello and Antonio Stabile Eur. Phys. J. C, 79 1 (2019) 41 Published online: 18 January 2019 DOI: 10.1140/epjc/s10052-019-6574-1