Ghosts in the self-accelerating DGP branch with Gauss–Bonnet effectYen-Wei Liu, Keisuke Izumi, Mariam Bouhmadi-López and Pisin ChenEur. Phys. J. C, 75 6 (2015) 248DOI: https://doi.org/10.1140/epjc/s10052-015-3463-0