Resonance instability of primordial gravitational waves during inflation in Chern–Simons gravity Chengjie Fu, Jing Liu, Tao Zhu, Hongwei Yu and Puxun Wu Eur. Phys. J. C, 81 3 (2021) 204 Published online: 01 March 2021 DOI: 10.1140/epjc/s10052-021-09001-2