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In loop quantum gravity the quantum states of a black hole horizon consist of pointlike discrete quantum geometry excitations (or punctures) labeled by spin j. The excitations possibly carry other internal degrees of freedom, and the associated quantum states are eigenstates of the area A operator. The appropriately scaled area operator A/(8πl) can also be interpreted as the physical Hamiltonian associated with the quasilocal stationary observers located at a small distance l from the horizon. Thus, the local energy is entirely accounted for by the geometric operator A. Assuming that: Close to the horizon the quantum state has a regular energy momentum tensor and hence the local temperature measured by stationary observers is the Unruh temperature. Degeneracy of matter states is exponential with the area exp (λA/l²p), which is supported by the well-established results of QFT in curved spacetimes, which do not determine A but assert an exponential behavior. The geometric excitations of the horizon (punctures) are indistinguishable. And finally that the semiclassical limit the area of the black hole horizon is large in Planck units. It follows that: Up to quantum corrections, matter degrees of freedom saturate the holographic bound, viz., λ must be equal to ¼ Up to quantum corrections, the statistical black hole entropy coincides with Bekenstein-Hawking entropy S = A/(4l²p). The number of horizon punctures goes like N ∝ ...\A/l²p-, i.e., the number of punctures N remains large in the semiclassical limit. Fluctuations of the horizon area are small ΔA/A ∝ (l²p/A)1/4, while fluctuations of the area of an individual puncture are large (large spins dominate). A precise notion of local conformai invariance of the thermal state is recovered in the A → ∝ limit where the near horizon geometry becomes Rindler. We also show how the present model (constructed from loop quantum gravity) provides a regularization of (and gives a concrete meaning to) the formal Gibbons-Hawking Euclidean path-integral treatment of the black hole system. These results offer a new scenario for semiclassical consistency of loop quantum gravity in the context of black hole physics, and suggest a concrete dynamical mechanism for large spin domination leading simultaneously to semiclassicality and continuity. [ABSTRACT FROM AUTHOR]

We study the linear perturbations about nonrotating black holes in the context of degenerate higher-order scalar-tensor (DHOST) theories, using a systematic approach that extracts the asymptotic behavior of perturbations (at spatial infinity and near the horizon) directly from the first-order radial differential system governing these perturbations. For axial (odd-parity) modes, this provides an alternative to the traditional approach based on a second-order Schrödinger-like equation with an effective potential, which we also discuss for completeness. For polar (even-parity) modes, which contain an additional degree of freedom in DHOST theories, and are thus more complex, we use a direct treatment of the four-dimensional first-order differential system (without resorting to a second order reformulation). We illustrate our study with two specific types of black hole solutions: "stealth" Schwarzschild black holes, with a nontrivial scalar hair, as well as a class of nonstealth black holes whose metric is distinct from Schwarzschild. The knowledge of the asymptotic behaviors of the perturbations enables us to compute numerically quasinormal modes, as we show explicitly for the nonstealth solutions. Finally, the asymptotic form of the modes also signals some pathologies in the stealth and nonstealth solutions considered here. [ABSTRACT FROM AUTHOR]

Using Monte Carlo simulations, we compute the integrated emission spectra of black holes in the framework of loop quantum gravity (LQG). The black hole emission rates are governed by the entropy whose value, in recent holographic loop quantum gravity models, was shown to agree at leading order with the Bekenstein-Hawking entropy. Quantum corrections depend on the Barbero-Immirzi parameter γ. Starting with black holes of initial horizon area A ~ 10² in Planck units, we present the spectra for different values of γ. Each spectrum clearly decomposes into two distinct parts: a continuous background which corresponds to the semiclassical stages of the evaporation and a series of discrete peaks which constitutes a signature of the deep quantum structure of the black hole. We show that γ has an effect on both parts that we analyze in detail. Finally, we estimate the number of black holes and the instrumental resolution required to experimentally distinguish between the considered models. [ABSTRACT FROM AUTHOR]

We study the thermodynamical properties of black holes when described as gases of indistinguishable punctures with a chemical potential. In this picture, which arises from loop quantum gravity, the black hole microstates are defined by finite families of half-integers spins coloring the punctures, and the near-horizon energy measured by quasilocal stationary observers defines the various thermodynamical ensembles. The punctures carry excitations of quantum geometry in the form of quanta of area, and the total horizon area aH is given by the sum of these microscopic contributions. We assume here that the system satisfies the Bose-Einstein statistics, and that each microstate is degenerate with a holographic degeneracy given by exp(λaH/l²P1) and λ > 0. We analyze in detail the thermodynamical properties resulting from these inputs, and in particular compute the grand canonical entropy. We explain why the requirements that the temperature be fixed to the Unruh temperature and that the chemical potential vanishes do not specify completely the semiclassical regime of large horizon area, and classify in turn what the various regimes can be. When the degeneracy saturates the holographic bound (λ = 1/4), there exists a semiclassical regime in which the subleading corrections to the entropy are logarithmic. Furthermore, this regime corresponds to a Bose-Einstein condensation, in the sense that it is dominated by punctures carrying the minimal (or ground state) spin value 1/2. [ABSTRACT FROM AUTHOR]