Eur. Phys. J. C (2021) 81: 576
https://doi.org/10.1140/epjc/s10052-021-09368-2

Regular Article - Theoretical Physics

Stability of Schwarzschild (Anti)de Sitter black holes in conformal gravity

¹ Istituto Nazionale di Fisica Nucleare, Sezione di Catania, 95123, Catania, Italy
² Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000, Prague 8, Czech Republic
³ Dipartimento di Fisica e Astronomia, Università di Catania, 95123, Catania, Italy
⁴ School of Nuclear Science and Technology, Lanzhou University, 222 South Tianshui Road, 730000, Lanzhou, China

^a daniele.lanteri@ct.infn.it

Received: 21 February 2021
Accepted: 23 June 2021
Published online: 3 July 2021

Abstract

We study the thermodynamics of spherically symmetric, neutral and non-rotating black holes in conformal (Weyl) gravity. To this end, we apply different methods: (i) the evaluation of the specific heat; (ii) the study of the entropy concavity; (iii) the geometrical approach to thermodynamics known as thermodynamic geometry; (iv) the Poincaré method that relates equilibrium and out-of-equilibrium thermodynamics. We show that the thermodynamic geometry approach can be applied to conformal gravity too, because all the key thermodynamic variables are insensitive to Weyl scaling. The first two methods, (i) and (ii), indicate that the entropy of a de Sitter black hole is always in the interval , whereas thermodynamic geometry suggests that, at , there is a second order phase transition to an Anti de Sitter black hole. On the other hand, we obtain from the Poincaré method (iv) that black holes whose entropy is are stable or in a saddle-point, whereas when they are always unstable, hence there is no definite answer on whether such transition occurs. Since thermodynamics geometry takes the view that the entropy is an extensive quantity, while the Poincaré method does not require extensiveness, it is valuable to present here the analysis based on both approaches, and so we do.