Ghosts in the self-accelerating DGP branch with Gauss–Bonnet effect Yen-Wei Liu, Keisuke Izumi, Mariam Bouhmadi-López and Pisin Chen Eur. Phys. J. C, 75 6 (2015) 248 Published online: 03 June 2015 DOI: 10.1140/epjc/s10052-015-3463-0