Wald entropy in Kaluza-Klein black holes

We study the thermodynamics of the 4-dimensional electrically charged black-hole solutions of the simplest 5-dimensional Kaluza-Klein theory using Wald's formalism. We show how the electric work term present in the 4-dimensional first law of black-hole thermodynamics arises in the purely gravitational 5-dimensional framework. In particular, we find an interesting geometric interpretation of the 4-dimensional electrostatic potential similar to the angular velocity in rotating black holes. Furthermore, we show how the momentum map equation arises from demanding compatibility between the timelike Killing vector of the black-hole solution and the spatial Killing vector of the 5-dimensional background.

Automated summary

In this study, we use Wald's formalism to investigate the thermodynamics of 4-dimensional electrically charged black-hole solutions in the simplest 5-dimensional Kaluza-Klein theory. We demonstrate how the electric work term, which is present in the 4-dimensional first law of black-hole thermodynamics, arises in the purely gravitational 5-dimensional framework. Additionally, we find an interesting geometric interpretation of the 4-dimensional electrostatic potential, similar to the angular velocity in rotating black holes. Furthermore, we show how the momentum map equation arises as a result of demanding compatibility between the timelike Killing vector of the black-hole solution and the spatial Killing vector of the 5-dimensional background.