Are ultraspinning Kerr-Sen-AdS4 black holes always superentropic?
Abstract
We study thermodynamics of the four-dimensional Kerr-Sen-AdS black hole and its ultraspinning counterpart and verify that both black holes fulfil the first law and Bekenstein-Smarr mass formulas of black hole thermodynamics. Furthermore, we derive new Christodoulou-Ruffini-like squared-mass formulas for the usual and ultraspinning Kerr-Sen-AdS4 solutions. We show that this ultraspinning Kerr-Sen-AdS4 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-AdS4 superentropic 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 (me≥8 l /√{27 } with l being the cosmological scale) both for the extremal ultraspinning Kerr-Sen-AdS4 black hole and for the extremal superentropic Kerr-Newman-AdS4 case, the former has a maximal horizon radius rHP=l /√{3 }, which is the minimum of the latter. Therefore, these two different kinds of four-dimensional ultraspinning charged AdS black holes exhibit some significant physical differences.
- Publication:
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Physical Review D
- Pub Date:
- August 2020
- DOI:
- 10.1103/PhysRevD.102.044007
- arXiv:
- arXiv:2007.02224
- Bibcode:
- 2020PhRvD.102d4007W
- Keywords:
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- General Relativity and Quantum Cosmology
- E-Print:
- 8 pages, to appear in PRD