Effects of the external string cloud on the Van der Waals like behavior and efficiency of AdS-Schwarzschild black holes in massive gravity

Abstract

In this paper we study AdS-Schwarzschild black holes in four and five dimensions in dRGT minimally coupled to a cloud of strings and investigate the effects of this string cloud on the thermodynamics of the black holes. It is observed that the entropy of the string cloud and massive terms does not affect the black hole entropy. The observations about four dimensions indicate that the massive term in the presence of external string cloud can not exhibit Van der Waals like behavior for AdS-Schwarzschild black holes and therefore there is only the Hawking-Page phase transition. In contrast, in five dimensions, the graviton mass modifies this behavior through the third massive term, so that a critical behavior and second order phase transition is deduced. Also, the Joule-Thomson effect is not observed. The black hole stability conditions are also studied in four and five dimensions and a critical value for the string cloud parameter is presented. In five dimensions a degeneracy between states for extremal black holes is investigated. After studying black holes as thermodynamic systems, we consider such systems as heat engines, and finally the efficiency of them is calculated.