Critical behavior of AdS Gauss–Bonnet massive black holes in the presence of external string cloud Hadi Ranjbari, Mehdi Sadeghi, M. Ghanaatian and Gh. Forozani Eur. Phys. J. C, 80 1 (2020) 17 Published online: 11 January 2020 DOI: 10.1140/epjc/s10052-019-7592-8