Evidence for NO violation of the second law in extended black hole thermodynamics

Abstract

The purpose of the current letter is to give some relevant clarification on the validity of the laws of thermodynamics and the stability of the horizon by scalar field scattering formalism. On the one side, the connection between the energy of the absorbed particle and the change of the enthalpy of the black hole appears to resolve the violation of the second law. On the other side, such connection stipulates a fixed rank of the gauge group $N$ in the boundary conformal field theory which is against the extended phase space spirit, where the cosmological constant is allowed to vary inducing a holographical dually changing of $N$. By recalling the Grand potential, we suggest more stringent conditions under which the second law holds taking into account the missing information about the variation of the cosmological constant ie. the pressure. Our result offers direct evidence of no violation of the second law in the extended phase space.