Gravitational waves from cosmic bubble collisions Dong-Hoon Kim, Bum-Hoon Lee, Wonwoo Lee, Jongmann Yang and Dong-han Yeom Eur. Phys. J. C, 75 3 (2015) 133 Published online: 20 March 2015 DOI: 10.1140/epjc/s10052-015-3348-2