Thermodynamic Geometry of Three-Dimensional Einstein–Maxwell-Dilaton Black Hole
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Eur. Phys. J. C (2018) 78:955 https://doi.org/10.1140/epjc/s10052-018-6434-4 Regular Article - Theoretical Physics Thermodynamic geometry of three-dimensional Einstein–Maxwell-dilaton black hole Xin-Yang Wanga, Ming Zhangb, Wen-Biao Liuc Department of Physics, Beijing Normal University, Beijing 100875, China Received: 7 May 2018 / Accepted: 11 November 2018 / Published online: 21 November 2018 © The Author(s) 2018 Abstract The thermodynamics of a three-dimensional there is a deeply connection between the black hole and ther- Einstein–Maxwell-dilaton black hole is investigated using modynamics. It was first noted that in AdS space, there exists the method of thermodynamic geometry. According to the a phase transition between the Schwarzschild anti-de-Sitter definition of thermodynamic geometry and the first law of the black hole and the thermal anti-de-Sitter space by Hawk- black hole, two-dimensional Ruppeiner and Quevedo geom- ing and Page [4], which is called the Hawking-Page phase etry are constructed respectively. Afterwards, both the scalar transition. This phenomenon can be explained as the confine- curvature and the extrinsic curvature of hypersurface at con- ment/deconfinement phase transition in QCD [3,5]. stant Q of the two-dimensional thermodynamic space are Recently, it is found that the charged AdS black hole has calculated. The results show that, the extrinsic curvature can the first order phase transition between a large black hole and play the role of heat capacity to locate the second-order criti- a small black hole [6–9]. With the temperature increasing, the cal point and determinate the stability of the black hole, which coexistence curve terminates at the critical point and the first is much better than the scalar curvature. However, for values order phase transition becomes the second order one. The of the entropy below that for which the specific heat diverges, behavior of the phase transition is quite similar to the van der the curve of the extrinsic curvature has an extra divergent Waals phase transition. point. Considering the fluctuation of the AdS radius, we can Subsequently, the AdS black hole thermodynamics can modify the first law of thermodynamics and reconstruct the be generally promoted to the extended phase space. It has three-dimensional Quevedo geometry. In this geometry, the been found that when the cosmological constant is consid- extrinsic curvature of the hypersurface at constant Q can ered as a thermodynamic variable, the more abundant phase replace the heat capacity to locate the second-order critical structure of the AdS black hole can be obtained [10–12]. point and determinate the stability of the black hole near the Therefore, the first law of thermodynamics is modified to the =−Λ critical point. In addition, the extra divergent point disap- form including the VdP term, where P 8π [13,14]. In pears. The results show that the AdS radius must be con- this context, the mass of black hole M is considered as the sidered as a variable when the thermodynamics of an AdS enthalpy rather than the internal energy. In 2012, Kubiznak black hole is investigated, so that the result can reflect the et al. [15] restudied the thermodynamic properties of charged real physics. AdS black holes in the extended phase space. They found that the black hole and the van der Waals system share the same P − V oscillatory behavior, critical exponents and equal area 1 Introduction law. Therefore, the AdS black hole and the van der Waals sys- tem can be identified in the extended phase space. Since then, The thermodynamics of black hole is one of the most excit- many works have studied the thermodynamic properties of ing and challenging topics in theoretical physics. Due to different AdS black holes [16–22]. AdS/CFT [1–3], the AdS black holes attract more and more On the other hand, the pioneering efforts by Weinhold attention. Especially in recent years, the research for the [23,24] and Ruppeiner [25,26] have shown that the equilib- space-time properties of the AdS black holes showed that rium space of a thermodynamic system can be considered as the Riemannian geometry and the metric derives from the a e-mail: [email protected] Gaussian fluctuation moments. Thermodynamic geometry is b e-mail: [email protected] a powerful tool for studying thermodynamic systems, which c e-mail: [email protected] 123 955 Page 2 of 12 Eur. Phys. J. C (2018) 78 :955 constructs an intimate connection between the description modified first law and the definition of the Quevedo geom- of thermodynamics and the description of statistics. In other etry, the new three-dimensional Quevedo geometry of the words, the thermodynamic geometry can construct an inti- black hole is reconstructed. And then the scalar curvature mate connection between the macrostate and the microstate. and the extrinsic curvature are calculated, respectively. The Riemann scalar curvature can be calculated when the The organization of the paper is as follows. In Sect. 2,we equilibrium space is established. The scalar curvature is pro- will review the solution of the three-dimensional Einstein– portional to the correlation volume of the thermodynamic Maxwell-dilaton black hole and the first law of thermody- system [26]. Therefore, the magnitude of scalar curvature can namics for the black hole. In Sect. 3, we combine the first reflect the interaction strength of microscopic particles in the law of thermodynamics with the thermodynamic metric to system. Meanwhile, the sign of the scalar curvature repre- construct the Ruppeiner and Quevedo geometry, and then sents the attraction or exclusion of the microscopic particles calculate both the scalar curvature and the extrinsic curva- in the system [26]. The method of the thermodynamic geom- ture of hypersurface at constant Q of two types of geome- etry can be applied to the black hole, to construct an intimate tries. Furthermore, we compare the two types of curvatures connection between the macroscopic state and the micro- with the heat capacity. In Sect. 4, we consider the fluctuation scopic state of the black hole. Although the method of ther- of AdS radius and modify the first law of thermodynamics. modynamic geometry has been applied to investigate phase Combining the modified first law with the definition of the transition of a black hole, the Ruppeiner scalar curvature Quevedo metric, we reconstruct the new Quevedo geometry can only expect the second-order phase transitions for some and calculate the scalar curvature and the extrinsic curvature special black holes [27–30]. However, for an arbitrary black of hypersurface at constant Q. The paper ends with conclu- hole, the scalar curvature in both the Weinhold and Rup- sions in Sect. 5. peiner geometry cannot completely locate the second-order critical point. Subsequent studies have found that the Wein- hold geometry is associated with the Ruppeiner geometry by 2 A three dimensional Einstein–Maxwell-dilaton black conformal transformation [31,32]. In order to avoid this dis- hole and the first law of thermodynamics advantage, another geometric formulation of thermodynam- ics was proposed by Quevedo [33,34]. Quevedo’s geometry In this section, we will review the three-dimensional Einstein– incorporates Legendre invariance in a natural way, and it Maxwell-dilaton black hole [36]. The scalar-tensor theory allows us to derive Legendre invariant metrics in the space has two equivalent formulations, which are Jordan and Ein- of equilibrium states. Some drawbacks in Weinhold and Rup- stein frames related by conformal transformation. In the Jor- peiner’s geometry can be avoided by Quevedo’s geometry. dan frame, the action is written in the way that the Ricci scalar However, the scalar curvature of Quevedo’s geometry also is multiplied by some functions of the scalar field. The gen- cannot completely locate the second-order critical points in eral form of the three-dimensional action of the scalar-tensor an arbitrary black hole yet. modified gravity theory in the Jordan frame can be expressed Afterwards, Mansoori et al. [35] investigated the extrin- as [37] sic curvature of hypersurface at constant Q in the Ruppeiner ( ) 1 geometry. They gave a general expression of the extrinsic I ST =− −˜gd3x[F(ψ)R˜ − 2U(ψ) curvature of the hypersurface. It was shown that the extrin- 16π μν ˜ ˜ ˜ sic curvature of the hypersurface can completely locate the + G(ψ)g˜ ∇μψ∇νψ − L(F)]. (1) second-order critical point and determinate the stability of μν ˜ μν ˜ the black hole. This shows that the extrinsic curvature can In which, g˜ is the space-time metric, R =˜g Rμν is the obtain more information than the method of scalar curvature. Ricci scalar, ψ is the scalar field, F(ψ), U(ψ) and G(ψ) are Therefore, we will use the method of extrinsic curvature to arbitrary functions of the scalar field. The covariant derivative ˜ study the thermodynamic geometry of the three-dimensional is denoted by ∇ in the Jordan frame. The electromagnetic ˜ ˜ ˜ ˜ αβ ˜ Einstein–Maxwell-dilaton black hole. Lagrangian L(F) =−F and F = F Fαβ is the Maxwell ˜ ˜ ρλ ρα λβ ˜ In this paper, based on the first law of thermodynam- invariant with Fαβ = ∂α Aβ − ∂β Aα and F =˜g g˜ Fαβ . ics and the definition of thermodynamic geometry, the two- Because of the strong coupling between the scalar and the dimensional Ruppeiner and Quevedo geometry are con- gravitational fields, the equation of motions for the action (1) structed. Afterwards, the scalar curvature and the extrin- is very difficult to solve. Therefore, we must translate it into sic curvature of hypersurfaces at constant Q are calculated the Einstein-dilaton action in the Einstein frame to simplify respectively. The difference between the heat capacity and the calculation.