HS in flat spacetime: the effective action method L. Bonora, M. Cvitan, P. Dominis Prester, S. Giaccari and T. Štemberga Eur. Phys. J. C, 79 3 (2019) 258 Published online: 21 March 2019 DOI: 10.1140/epjc/s10052-019-6660-4