
Acena, A., Anabalon, A., & Astefanesei, D. (2013). Exact hairy black brane solutions in 5D antide Sitter space and holographic renormalization group flows. Phys. Rev. D, 87(12), 6 pp.
Abstract: We construct a general class of exact regular black hole solutions with toroidal horizon topology in fivedimensional antide Sitter gravity with a selfinteracting scalar field. With these boundary conditions and due to the nontrivial backreaction of the scalar field, the nohair theorems can be evaded so that an event horizon can be formed. The scalar field is regular everywhere outside the curvature singularity and it vanishes at the boundary where the potential is finite. We study the properties of these black holes in the context ofAdS/CFT duality and comment on the dual operators, which saturate the unitarity bound. We present exact expressions for the beta function and construct a cfunction that characterizes the renormalizationgroup flow.



Anabalon, A., & Batista, C. (2016). A class of integrable metrics. Phys. Rev. D, 93(6), 13 pp.
Abstract: In four dimensions, the most general metric admitting two commuting Killing vectors and a ranktwo Killing tensor can be parametrized by ten arbitrary functions of a single variable. We show that picking a special vierbein, reducing the system to eight functions, implies the existence of two geodesic and sharefree, null congruences, generated by two principal null directions of the Weyl tensor. Thus, if the spacetime is an Einstein manifold, the GoldbergSachs theorem implies it is Petrov type D, and by explicit construction, is in the Carter class. Hence, our analysis provides a straightforward connection between the most general integrable structure and the Carter family of spacetimes.



Anabalon, A., & Cisterna, A. (2012). Asymptotically (anti) de Sitter black holes and wormholes with a selfinteracting scalar field in four dimensions. Phys. Rev. D, 85(8), 6 pp.
Abstract: The aim of this paper is to report on the existence of a wide variety of exact solutions, ranging from black holes to wormholes, when a conformally coupled scalar field with a selfinteracting potential containing a linear, a cubic and a quartic self interaction is taken as a source of the energymomentum tensor, in the Einstein theory with a cosmological constant. Among all the solutions there are two particularly interesting. On the one hand, the spherically symmetric black holes when the cosmological constant is positive; they are shown to be everywhere regular, namely, there is no singularity neither inside nor outside the event horizon. On the other hand, there are spherically symmetric and topological wormholes that connect two asymptotically (anti) de Sitter regions with a different value for the cosmological constant. The regular black holes and the wormholes are supported by everywhere regular scalar field configurations.



Anabalon, A., & Deruelle, N. (2013). Mechanical stability of asymptotically flat black holes with minimally coupled scalar hair. Phys. Rev. D, 88(6), 9 pp.
Abstract: We show that the asymptotically flat hairy black holes, solutions of the Einstein field equations minimally coupled to a scalar field, previously discovered by one of us, present mode instability against linear radial perturbations. It is also shown that the number of unstable modes is finite and their frequencies can be made arbitrarily small.



Anabalon, A., & Oliva, J. (2012). Exact hairy black holes and their modification to the universal law of gravitation. Phys. Rev. D, 86(10), 5 pp.
Abstract: In this paper two things are done. First, it is pointed out the existence of exact asymptotically flat, spherically symmetric black holes when a selfinteracting, minimally coupled scalar field is the source of the Einstein equations in four dimensions. The scalar field potential is recently found to be compatible with the hairy generalization of the PlebanskiDemianski solution of general relativity. This paper describes the spherically symmetric solutions that smoothly connect the Schwarzschild black hole with its hairy counterpart. The geometry and scalar field are everywhere regular except at the usual Schwarzschildlike singularity inside the black hole. The scalar field energy momentum tensor satisfies the nullenergy condition in the static region of spacetime. The first law holds when the parameters of the scalar field potential are fixed under thermodynamical variation. Second, it is shown that an extra, dimensionless parameter, present in the hairy solution, allows to modify the gravitational field of a spherically symmetric black hole in a remarkable way. When the dimensionless parameter is increased, the scalar field generates a flat gravitational potential that, however, asymptotically matches the Schwarzschild gravitational field. Finally, it is shown that a positive cosmological constant can render the scalar field potential convex if the parameters are within a specific rank.



Anabalon, A., Astefanesei, D., & Martinez, C. (2015). Mass of asymptotically antide Sitter hairy spacetimes. Phys. Rev. D, 91(4), 6 pp.
Abstract: In the standard asymptotic expansion of fourdimensional static asymptotically flat spacetimes, the coefficient of the first subleading term of the lapse function can be identified with the mass of the spacetime. Using the Hamiltonian formalism we show that, in asymptotically locally antide Sitter spacetimes endowed with a scalar field, the mass can read off in the same way only when the boundary conditions are compatible with the asymptotic realization of the antide Sitter symmetry. Since the mass is determined only by the spatial metric and the scalar field, the above effect appears by considering not only the constraints, but also the dynamic field equations, which relate the spatial metric with the lapse function. In particular, this result implies that some prescriptions for computing the mass of a hairy spacetime are not suitable when the scalar field breaks the asymptotic antide Sitter invariance.



Anabalon, A., Bicak, J., & Saavedra, J. (2014). Hairy black holes: Stability under oddparity perturbations and existence of slowly rotating solutions. Phys. Rev. D, 90(12), 6 pp.
Abstract: We show that, independently of the scalar field potential and of specific asymptotic properties of the spacetime (asymptotically flat, de Sitter or antide Sitter), any static, spherically symmetric or planar, black hole solution of the Einstein theory minimally coupled to a real scalar field with a general potential is mode stable under linear oddparity perturbations. To this end, we generalize the ReggeWheeler equation for a generic selfinteracting scalar field, and show that the potential of the relevant Schrodinger operator can be mapped, by the socalled Sdeformation, to a semipositively defined potential. With these results at hand we study the existence of slowly rotating configurations. The frame dragging effect is compared with the corresponding effect in the case of a Kerr black hole.



Anabalon, A., Canfora, F., Giacomini, A., & Oliva, J. (2011). Black holes with gravitational hair in higher dimensions. Phys. Rev. D, 84(8), 10 pp.
Abstract: A new class of vacuum black holes for the most general gravity theory leading to second order field equations in the metric in even dimensions is presented. These spacetimes are locally antide Sitter in the asymptotic region, and are characterized by a continuous parameter that does not enter in the conserve charges, nor it can be reabsorbed by a coordinate transformation: it is therefore a purely gravitational hair. The black holes are constructed as a warped product of a twodimensional spacetime, which resembles the rt plane of the BanadosTeitelboimZanelli black hole, times a warp factor multiplying the metric of a D – 2dimensional Euclidean base manifold, which is restricted by a scalar equation. It is shown that all the Noether charges vanish. Furthermore, this is consistent with the Euclidean action approach: even though the black hole has a finite temperature, both the entropy and the mass vanish. Interesting examples of base manifolds are given in eight dimensions which are products of Thurston geometries, giving then a nontrivial topology to the black hole horizon. The possibility of introducing a torsional hair for these solutions is also discussed.



Anabalon, A., Canfora, F., Giacomini, A., & Oliva, J. (2011). Gribov ambiguity in asymptotically AdS threedimensional gravity. Phys. Rev. D, 83(6), 7 pp.
Abstract: In this paper the zero modes of the de Donder gauge FaddeevPopov operator for threedimensional gravity with negative cosmological constant are analyzed. It is found that the AdS(3) vacuum produces (infinitely many) normalizable smooth zero modes of the FaddeevPopov operator. On the other hand, it is found that the BanadosTeitelboimZanelli black hole (including the zero mass black hole) does not generate zero modes. This differs from the usual Gribov problem in QCD where, close to the maximally symmetric vacuum, the FaddeevPopov determinant is positive definite while "far enough'' from the vacuum it can vanish. This suggests that the zero mass BanadosTeitelboimZanelli black hole could be a suitable ground state of threedimensional gravity with negative cosmological constant. Because of the kinematic origin of this result, it also applies for other covariant gravity theories in three dimensions with AdS(3) as maximally symmetric solution, such as new massive gravity and topologically massive gravity. The relevance of these results for supersymmetry breaking is pointed out.



Anabalon, A., Cisterna, A., & Oliva, J. (2014). Asymptotically locally AdS and flat black holes in Horndeski theory. Phys. Rev. D, 89(8), 9 pp.
Abstract: In this paper we construct asymptotically locally AdS and flat black holes in the presence of a scalar field whose kinetic term is constructed out from a linear combination of the metric and the Einstein tensor. The field equations as well as the energymomentum tensor are second order in the metric and the field, therefore the theory belongs to the ones defined by Horndeski. We show that in the presence of a cosmological term in the action, it is possible to have a real scalar field in the region outside the event horizon. The solutions are characterized by a single integration constant, the scalar field vanishes at the horizon and it contributes to the effective cosmological constant at infinity. We extend these results to the topological case. The solution is disconnected from the maximally symmetric AdS background, however, within this family there exists a gravitational soliton which is everywhere regular. This soliton is therefore used as a background to define a finite Euclidean action and to obtain the thermodynamics of the black holes. For a certain region in the space of parameters, the thermodynamic analysis reveals a critical temperature at which a HawkingPage phase transition between the black hole and the soliton occurs. We extend the solution to arbitrary dimensions greater than 4 and show that the presence of a cosmological term in the action allows one to consider the case in which the standard kinetic term for the scalar it is not present. In such a scenario, the solution reduces to an asymptotically flat black hole.



Aros, R., & Contreras, M. (2006). Torsion induces gravity. Phys. Rev. D, 73(8), 4 pp.
Abstract: In this work the PoincareChernSimons and antide SitterChernSimons gravities are studied. For both, a solution that can be cast as a black hole with manifest torsion is found. Those solutions resemble Schwarzschild and SchwarzschildAdS solutions, respectively.



Asenjo, F. A., & Hojman, S. A. (2017). Birefringent light propagation on anisotropic cosmological backgrounds. Phys. Rev. D, 96(4), 12 pp.
Abstract: Exact electromagnetic wave solutions to Maxwell equations on anisotropic Bianchi I cosmological spacetime backgrounds are studied. The waves evolving on Bianchi I spacetimes exhibit birefringence (associated with linear polarization) and dispersion. The particular case of a vacuumdominated anisotropic Universe, which reproduces a FriedmannRobertsonWalker Universe (for late times)while, for earlier times, it matches a Kasner Universeis studied. The electromagnetic waves do not, in general, follow null geodesics. This produces a modification of the cosmological redshift, which is then dependent on light polarization, its dispersion, and its nonnull geodesic behavior. New results presented here may help to tackle some issues related to the “horizon” problem.



Bunster, C., & Gomberoff, A. (2017). Gravitational domain walls and the dynamics of the gravitational constant G. Phys. Rev. D, 96(2), 9 pp.
Abstract: From the point of view of elementary particle physics the gravitational constant G is extraordinarily small. This has led to ask whether it could have decayed to its present value from an initial one commensurate with microscopical units. A mechanism that leads to such a decay is proposed herein. It is based on assuming that G may take different values within regions of the universe separated by a novel kind of domain wall, a “Gwall”. The idea is implemented by introducing a gauge potential A, and its conjugate D, which determines the value of G as an integration constant rather than a fundamental constant. The value of G jumps when one goes through a Gwall. The procedure extends one previously developed for the cosmological constant, but the generalization is far from straightforward: (i) The intrinsic geometry of a Gwall is not the same as seen from its two sides, because the second law of black hole thermodynamics mandates that the jump in G must cause a discontinuity in the scale of length. (ii) The size of the decay step in G is controlled by a function G(D) which may be chosen so as to diminish the value of G towards the asymptote G = 0, without fine tuning. It is shown that: (i) The dynamics of the gravitational field with G treated as a dynamical variable, coupled to Gwalls and matter, follows from an action principle, which is given. (ii) A particle that impinges on a Gwall may be refracted or reflected. (iii) The various forces between two particles change when a Gwall is inserted in between them. (iv) Gwalls may be nucleated trough tunneling and thermal effects. The semiclassical probabilities are evaluated. (v) If the action principle is constructed properly, the entropy of a black hole increases when the value of the gravitational constant is changed through the absorption of a Gwall by the hole.



Concha, P. K., Durka, R., Inostroza, C., Merino, N., & Rodriguez, E. K. (2016). Pure Lovelock gravity and ChernSimons theory. Phys. Rev. D, 94(2), 14 pp.
Abstract: We explore the possibility of finding pure Lovelock gravity as a particular limit of a ChernSimons action for a specific expansion of the AdS algebra in odd dimensions. We derive in detail this relation at the level of the action in five and seven dimensions. We provide a general result for higher dimensions and discuss some issues arising from the obtained dynamics.



Hojman, S. A., & Asenjo, F. A. (2015). Supersymmetric Majorana quantum cosmologies. Phys. Rev. D, 92(8), 7 pp.
Abstract: The Einstein equations for an isotropic and homogeneous FriedmannRobertsonWalker universe in the presence of a quintessence scalar field are shown to be described in a compact way, formally identical to the dynamics of a relativistic particle moving on a twodimensional spacetime. The correct Lagrangian for the system is presented and used to construct a spinor quantum cosmology theory using Breit's prescription. The theory is supersymmetric when written in the Majorana representation. The spinor field components interact through a potential that correlates the spacetime metric and the quintessence. An exact supersymmetric solution for k = 0 case is exhibited. This quantum cosmology model may be interpreted as a theory of interacting universes.



Hojman, S. A., & Asenjo, F. A. (2016). Comment on “Highly relativistic spingravity coupling for fermions”. Phys. Rev. D, 93(2), 4 pp.
Abstract: We exhibit difficulties of different sorts which appear when using the MathissonPapapetrou equations, in particular in the description of highly relativistic particles presented in R. Plyatsko and M. Fenyk [Phys. Rev. D 91, 064033 (2015)]. We compare some results of this theory and of the aforementioned work with the ones obtained using a Lagrangian formulation for massive spinning particles and show that the issues mentioned in the preceding sentence do not appear in the Lagrangian treatment.

