Rotating hairy black holes

We construct stationary black-hole solutions in SU(2) Einstein-Yang-Mills theory which carry angular momentum and electric charge. Possessing nontrivial non-Abelian magnetic fields outside their regular event horizon, they represent nonperturbative rotating hairy black holes.     

Investigation the geodesic motion of three dimensional rotating black holes

We study the geodesic equations in the space-time of neutral Brans–Dicke Dilaton black hole in three dimensions and BTZ black hole. We use the process of separation of the Hamilton–Jacobi equation to obtain the constants of motion. The whole analytical solution of the geodesic equations in the space-times of the intended black holes are shown completely. Moreover, the geodesic equations are solved in terms of Weierstrass elliptic functions. Furthermore, with use of the analytical solution and effective potential technique some trajectories around the black holes are classified. Meanwhile, by analytical solution, effective potential and considering the zeroes of underlying polynomials, some possible orbits are plotted. Finally, we compare our results with Cruz et. al. [17] and we indicate the benefits of the analytical method which is applied in this paper.     

Lower dimensional black holes

A survey of black hole physics in two spacetime dimensions is presented. Basic properties, specific solutions and quantum aspects are considered in turn. The relationship between string theoretic black holes and those arising in other (1+l)-dimensional theories of gravity is discussed.     

Holographic effective actions from black holes

Using the Wald?s relation between the Noether charge of diffeomorphisms and the entropy for a generic spacetime possessing a bifurcation surface, we introduce a method to obtain a family of higher order derivatives effective actions from the entropy of black holes. We consider the entropy as the starting point and we analyze the procedure of derivation of the action functional. We specialize to a particular class of theories which simplifies the calculations, f(R) theories. We apply the procedure to loop quantum gravity and to a general class of log-corrected entropy formulas.     

Supersymmetric coloured/hairy black holes

We discuss all possible spherically symmetric black hole type solutions to an N=2 supergravity model with SO(3) gauging. The solutions consist of a one parameter family of black hole solutions evading the no-hair theorem and an isolated solution that is a supersymmetric analogue of a coloured black hole.     

Holographic superconductor in the analytic hairy black hole

We study the charged black hole of hyperbolic horizon with scalar hair (charged Martinez-Troncoso-Zanelli: CMTZ black hole) as a model of analytic hairy black hole for holographic superconductor. For this purpose, we investigate the second order phase transition between CMTZ and hyperbolic Reissner-Nordström-AdS (HRNAdS) black holes. However, this transition unlikely occurs. As an analytic treatment for holographic superconductor, we develop superconductor in the bulk and superfluidity on the boundary using the CMTZ black hole below the critical temperature. The presence of charge destroys the condensates around the zero temperature, which is in accord with the thermodynamic analysis of the CMTZ black hole.     

The motion of black holes

The motion of axisymmetric non rotating black holes is discussed using the properties of Weyl solutions. It is shown that there are no such solutions representing more than one black hole or black holes and ordinary massive bodies apart from the exceptional case of a massive body which surrounds or partially surrounds a black hole. A new exact solution is obtained representing a black hole chased by a negative mass particle, both objects being uniformly accelerated and all solutions representing a single black hole tidally distorted by an external static, axisymmetric gravitational field are obtained.     

Thermodynamics of higher dimensional black holes

We discuss the thermodynamics of higher dimensional black holes with particular emphasis on a new class of spinning black holes which, due to the increased number of Casimir invariants, have additional spin degrees of freedom. In suitable limits, analytic solutions in arbitrary dimensions are presented for their temperature, entropy, and specific heat. In 5 + 1 and 9 + 1 dimensions, more general forms for these quantities are given. It is shown that the specific heat for a higher dimensional black hole is negative definite if it has only one non-zero spin parameter, regardless of the value of this parameter. We also consider equilibrium configurations with both massless particles and massive string modes.     

Geometrothermodynamics of higher dimensional black holes

We study the thermodynamics and geometrothermodynamics of different black hole configurations in more than four spacetime dimensions. We use the response functions to find the conditions under which second order phase transitions occur in higher-dimensional static Reissner–Nordström and stationary Kerr black holes. Our results indicate that the equilibrium manifold of all these black hole configurations is in general curved and that curvature singularities appear exactly at those places where second order phase transitions occur.     

Greybody factors of charged dilaton black holes in 2 + 1 dimensions

We have studied the scalar perturbation of charged dilaton black holes in 2+1 dimensions. The black hole considered here is a solution to the low-energy string theory in 2+1 dimensions. The exact decay rates and the grey body factors for the massless minimally coupled scalar is computed for both the charged and the uncharged dilaton black holes. The charged and the uncharged black hole show similar behavior for grey body factors, reflection coefficients and decay rates.This revised version was published online in April 2005. The publishing date was inserted.     

Holographic heat engine efficiency of hyperbolic charged black holes

We consider a four-dimensional charged hyperbolic black hole as working matter to establish a black hole holographic heat engine, and use the rectangular cycle to obtain the heat engine efficiency. We find that when the increasing of entropy is zero, the heat engine efficiency of the hyperbolic black hole becomes the well-known Carnot efficiency. We also find that less charge corresponds to higher efficiency in the case of $\tilde{q}>0$. Furthermore, we study the efficiency of the flat case and spherical case and compare the efficiency with that of the hyperbolic charged black holes. Finally, we use numerical simulation to study the efficiency in benchmark scheme.     

Gravitational decoupling for hairy black holes in asymptotic AdS spacetimes

In this study, the gravitational decoupling approach via extended geometric deformation is utilized to generate analytical black hole solutions owing to its simplicity and effectiveness. Considering the external fields surrounding Schwarzschild AdS black holes, we derive hairy black hole solutions in asymptotic AdS spacetime, satisfying the strong and dominant energy conditions. Moreover, we find that if the black hole spacetime is a fluid system, the fluid under each of these conditions is anisotropic.     

Higher dimensional charged rotating dilaton black holes

In this paper, we present the metric for the n-dimensional charged slowly rotating dilaton black hole with N = [(n −1)/2] independent rotation parameters, associated with N orthogonal planes of rotation in the background of asymptotically flat and asymptotically (anti)-de Sitter spacetime. The mass, angular momentum and the gyromagnetic ratio of such a black hole are determined for the arbitrary values of the dilaton coupling constant. We find that the gyromagnetic ratio crucially depends on the dilaton coupling constant, α, and decreases with increasing α in any dimension.     

Scalar hairy black holes and solitons in a gravitating Goldstone model

We study black hole solutions of Einstein gravity coupled to a specific global symmetry breaking Goldstone model described by an O(3) isovector scalar field in four spacetime dimensions. Our configurations are static and spherically symmetric, approaching at infinity a Minkowski spacetime background. A set of globally regular, particle-like solutions are found in the limit of vanishing event horizon radius. These configurations can be viewed as ‘regularised’ global monopoles, since their mass is finite and the spacetime geometry has no deficit angle. As an unusual feature, we notice the existence of extremal black holes in this model defined in terms of gravity and scalar fields only.     

Note on the motion of black holes

It is shown that from the point of view of a distant observer the gravitational field of a moving Schwarzschild black hole is the same as produced by an extended, non-rotating, spherical body of the same mass. According to him, a black hole follows the Newtonian equations of motion, though some quantities, for example the distance, lose their Newtonian meaning.