Search results for "black hole"
showing 10 items of 336 documents
Hawking Radiation by Kerr Black Holes and Conformal Symmetry
2010
The exponential blueshift associated with the event horizon of a black hole makes conformal symmetry play a fundamental role in accounting for its thermal properties. Using a derivation based on two-point functions, we show that the full spectrum of thermal radiation of scalar particles by Kerr black holes can be explicitly derived on the basis of a conformal symmetry arising in the wave equation near the horizon. The simplicity of our approach emphasizes the depth of the connection between conformal symmetry and black hole radiance.
Super-entropic black hole with Immirzi hair
2020
In the context of $f(R)$ generalizations to the Holst action, endowed with a dynamical Immirzi field, we derive an analytic solution describing asymptotically anti--de Sitter black holes with hyperbolic horizon. These exhibit a scalar hair of the second kind, which ultimately depends on the Immirzi field radial behavior. In particular, we show how the Immirzi field modifies the usual entropy law associated to the black hole. We also verify that the Immirzi field boils down to a constant value in the asymptotic region, thus restoring the standard loop quantum gravity picture. We finally prove the violation of the reverse isoperimetric inequality, resulting in the superentropic nature of the …
Rotating black holes in Eddington-inspired Born-Infeld gravity: an exact solution
2020
We find an exact, rotating charged black hole solution within Eddington-inspired Born-Infeld gravity. To this end we employ a recently developed correspondence or {\it mapping} between modified gravity models built as scalars out of contractions of the metric with the Ricci tensor, and formulated in metric-affine spaces (Ricci-Based Gravity theories) and General Relativity. This way, starting from the Kerr-Newman solution, we show that this mapping bring us the axisymmetric solutions of Eddington-inspired Born-Infeld gravity coupled to a certain model of non-linear electrodynamics. We discuss the most relevant physical features of the solutions obtained this way, both in the spherically sym…
Black hole solutions of N=2, d=4 supergravity with a quantum correction, in the H-FGK formalism
2012
We apply the H-FGK formalism to the study of some properties of a general class of black holes in N = 2 supergravity in four dimensions that correspond to the harmonic and hyperbolic ansatze and we obtain explicit extremal and non-extremal solutions for the t(3) model with and without a quantum correction. Not all solutions of the corrected model (quantum black holes), including in particular a solution with a single q(1) charge, have a regular classical limit.
Quantum Gravity Effects in the Kerr Spacetime
2010
We analyze the impact of the leading quantum gravity effects on the properties of black holes with nonzero angular momentum by performing a suitable renormalization group improvement of the classical Kerr metric within Quantum Einstein Gravity (QEG). In particular we explore the structure of the horizons, the ergosphere, and the static limit surfaces as well as the phase space avilable for the Penrose process. The positivity properties of the effective vacuum energy momentum tensor are also discussed and the "dressing" of the black hole's mass and angular momentum are investigated by computing the corresponding Komar integrals. The pertinent Smarr formula turns out to retain its classical f…
Nonsingular electrovacuum solutions with dynamically generated cosmological constant
2013
We consider static spherically symmetric configurations in a Palatini extension of General Relativity including R-2 and Ricci-squared terms, which is known to replace the central singularity by a wormhole in the electrovacuum case. We modify the matter sector of the theory by adding to the usual Maxwell term a nonlinear electromagnetic extension which is known to implement a confinement mechanism in flat space. One feature of the resulting theory is that the nonlinear electric field leads to a dynamically generated cosmological constant. We show that with this matter source the solutions of the model are asymptotically de Sitter and possess a wormhole topology. We discuss in some detail the…
Mass spectrum and thermodynamics of quasi-conformal gauge theories from gauge/gravity duality
2011
We use gauge/gravity duality to study simultaneously the mass spectrum and the thermodynamics of a generic quasi-conformal gauge theory, specified by its beta function. The beta function of a quasi-conformal theory almost vanishes, and the coupling is almost constant between two widely separated energy scales. Depending on whether the gravity dual has a black hole or not, the mass spectrum is either a spectrum of quasinormal oscillations or a normal T=0 mass spectrum. The mass spectrum is quantitatively correlated with the thermal properties of the system. As the theory approaches conformality, the masses have to vanish. We show that in this limit, the masses calculated via gauge/gravity du…
Two-point functions with an invariant Planck scale and thermal effects
2008
Nonlinear deformations of relativistic symmetries at the Planck scale are usually addressed in terms of modified dispersion relations. We explore here an alternative route by directly deforming the two-point functions of an underlying field theory. The proposed deformations depend on a length parameter (Planck length) and preserve the basic symmetries of the corresponding theory. We also study the physical consequences implied by these modifications at the Planck scale by analyzing the response function of an accelerated detector in Minkowski space, an inertial one in de Sitter space, and also in a black hole spacetime.
Short-distance contribution to the spectrum of Hawking radiation
2006
The Hawking effect can be rederived in terms of two-point functions and in such a way that it makes it possible to estimate, within the conventional semiclassical theory, the contribution of ultrashort distances to the Planckian spectrum. For Schwarzschild black holes of three solar masses the analysis shows that Hawking radiation is very robust up to frequencies of 96 T_H or 270 T_H for bosons and fermions, respectively. For primordial black holes (with masses around 10^{15} g) these frequencies turn out to be of order 52T_H and 142 T_H. Only at these frequencies and above do we find that the contribution of Planck distances is of order of the total spectrum itself. Below this scale, the c…
Low-energy scattering of extremal black holes by neutral matter
2002
We investigate the decay of a spherically symmetric near-extremal charged black hole, including back-reaction effects, in the near-horizon region. The non-locality of the effective action controlling this process allows and also forces us to introduce a complementary set of boundary conditions which permit to determine the asymptotic late time Hawking flux. The evaporation rate goes down exponentially and admits an infinite series expansion in Planck's constant. At leading order it is proportional to the total mass and the higher order terms involve higher order momenta of the classical stress-tensor. Moreover we use this late time behaviour to go beyond the near-horizon approximation and c…