Are ultra-spinning Kerr-Sen-AdS${}_4$ black holes always super-entropic ?

Abstract

We study thermodynamics of the four-dimensional Kerr-Sen-AdS black hole and its ultra-spinning counterpart, and verify that both black holes fullfil the first law and Bekenstein-Smarr mass formulae of black hole thermodynamics. Furthermore, we derive new Christodoulou-Ruffini-like squared-mass formulae for the usual and ultra-spinning Kerr-Sen-AdS${}_4$ solutions. We show that this ultra-spinning Kerr-Sen-AdS${}_4$ black hole does not always violate the Reverse Isoperimetric Inequality (RII) since the value of the isoperimetric ratio can be larger/smaller than, or equal to unity, depending upon where the solution parameters lie in the parameters space. This property is obviously different from that of the Kerr-Newman-AdS${}_4$ super-entropic black hole, which always strictly violates the RII, although both of them have some similar properties in other aspects, such as horizon geometry and conformal boundary. In addition, it is found that while there exists the same lower bound on mass ($m_e⩾8l/\sqrt{27}$ with $l$ being the cosmological scale) both for the extremal ultra-spinning Kerr-Sen-AdS${}_4$ black hole and for the extremal super-entropic Kerr-Newman-AdS${}_4$ case, the former has a maximal horizon radius: $r_{\mathrm{HP}}=l/\sqrt{3}$ which is the minimum of the latter. Therefore, these two different kinds of four-dimensional ultra-spinning charged AdS black holes exhibit some significant physical differences .

8 pages, to appear in PRD

References in corpus (5)

• Black Hole Enthalpy and an Entropy Inequality for the Thermodynamic Volume
• The first laws of thermodynamics of the (2+1)-dimensional BTZ black holes and Kerr-de Sitter spacetimes
• Notes on thermodynamics of super-entropic AdS black holes
• The correspondence between thermodynamic curvature and isoperimetric theorem from ultraspinning black hole
• Ultra-Spinning Gauged Supergravity Black Holes and their Kerr/CFT Correspondence