Thermodynamic instability of 3D Einstein-Born-Infeld AdS black holes

Super-entropic black holes possess finite-area but noncompact event horizons and violate the reverse iso-perimetric inequality.It has been conjectured that such black holes always have negative specific heat at constant volume C_(V)or negative specific heat at constant pressure C_(p)whenever Cy>0,making them unstable in extended thermodynamics.In this paper,we describe a test of this instability conjecture with a family of nonlinear electro-dynamic black holes,namely 3D Einstein-Bom-Infeld(EBI)AdS black holes.Our results show that when nonlinear electrodynamics effects are weak,the instability conjecture is valid.However,the conjecture can be violated in some parameter region when nonlinear electrodynamics effects are strong enough.This observation thus provides a counter example to the instability conjecture,which suggests that super-entropic black holes may be thermodynamically stable.

Thermodynamics for higher dimensional rotating black holes with variable Newton constant

The extensivity for the thermodynamics of general D-dimensional rotating black holes with or without a cosmological constant can be proved analytically,provided that the effective number of microscopic degrees of freedom and the chemical potential are given respectively as N=L^(D−2)/G,μ=GTI_(D)/L^(D−2),where G is the variable Newton constant,I_(D) is the Euclidean action,and L is a constant length scale.In the cases without a cosmological constant,i.e.,the Myers-Perry black holes,the physical mass and the intensive variables can be expressed as explicit macro state functions in the extensive variables in a simple and compact form,which allows for an analytical calculation of the heat capacity.The results indicate that the Myers-Perry black holes with zero,one,and k equal rotation parameters are all thermodynamically unstable.