Double Higgs boson production and Higgs self-coupling extraction at CLIC Philipp Roloff, Ulrike Schnoor, Rosa Simoniello and Boruo Xu Eur. Phys. J. C, 80 11 (2020) 1010 Published online: 02 November 2020 DOI: 10.1140/epjc/s10052-020-08567-7