Topology of higher-dimensional black holes' thermodynamics in massive gravity
In the recent work [Phys. Rev. Lett. 129, 191101 (2022)], the topological number was found to be a universal number independent of the black hole's parameters. In this paper, we study topological numbers for five-, six- and seven-dimensional anti-de Sitter black holes in the ghost-free massive gravity. We find that when the black holes are charged, they have the same topological number, and this number is independent of their parameters' values. For the uncharged black holes, their topological numbers are 0 or 1, and the specific values are determined by the values of the black holes' parameters. Since $k$ and $c_ 0^2c_2 m^2 $ appear together in the generalized free energy in the form of $k +c_ 0^2c_2 m^2 $, where $k$ characterizes the horizon curvature and $c_2 m^2 $ is the coefficient of the second term of massive potential associated with the graviton mass, this result is applicable to the black holes with the spherical, Ricci flat or hyperbolic horizons. This work shows that the parameters of the ghost-free massive gravity play an important role in the topological classes of black holes.