Spinning Loop Black Holes

In this paper we construct four Kerr-like spacetimes starting from the loop black hole Schwarzschild solutions (LBH) and applying the Newman-Janis transformation. In previous papers the Schwarzschild LBH was obtained replacing the Ashtekar connection with holonomies on a particular graph in a minisuperspace approximation which describes the black hole interior. Starting from this solution, we use a Newman-Janis transformation and we specialize to two different and natural complexifications inspired from the complexifications of the Schwarzschild and Reissner-Nordstrom metrics. We show explicitly that the space-times obtained in this way are singularity free and thus there are no naked singularities. We show that the transformation move, if any, the causality violating regions of the Kerr metric far from r=0. We study the space-time structure with particular attention to the horizons shape. We conclude the paper with a discussion on a regular Reissner-Nordstrom black hole derived from the Schwarzschild LBH and then applying again the Newmann-Janis transformation.Comment: 18 pages, 18 figure

Entropy of the Schwarzschild black hole to all orders in the Planck length

Considering corrections to all orders in the Planck length on the quantum state density from a generalized uncertainty principle (GUP), we calculate the statistical entropy of the scalar field on the background of the Schwarzschild black hole without any cutoff. We obtain the entropy of the massive scalar field proportional to the horizon area.Comment: 13 pages, 1 figure; Minor typos corrected, one reference added; Accepted for publication in Phys. Lett.

Noncommutative Solitons of Gravity

We investigate a three-dimensional gravitational theory on a noncommutative space which has a cosmological constant term only. We found various kinds of nontrivial solutions, by applying a similar technique which was used to seek noncommutative solitons in noncommutative scalar field theories. Some of those solutions correspond to bubbles of spacetimes, or represent dimensional reduction. The solution which interpolates $G_{\mu\nu}=0$ and Minkowski metric is also found. All solutions we obtained are non-perturbative in the noncommutative parameter $\theta$, therefore they are different from solutions found in other contexts of noncommutative theory of gravity and would have a close relation to quantum gravity.Comment: 29 pages, 5 figures. v2: minor corrections done in Section 3.1 and Appendix, references added. v3, v4: typos correcte

Noncommutative Geometry Inspired Rotating Black Hole in Three Dimensions

We find a new rotating black hole in three-dimensional anti-de Sitter space using an anisotropic perfect fluid inspired by the noncommutative black hole. We deduce the thermodynamical quantities of this black hole and compare them with those of a rotating BTZ solution.Comment: 7 page

Regular black hole in three dimensions

We find a new black hole in three dimensional anti-de Sitter space by introducing an anisotropic perfect fluid inspired by the noncommutative black hole. This is a regular black hole with two horizons. We compare thermodynamics of this black hole with that of non-rotating BTZ black hole. The first-law of thermodynamics is not compatible with the Bekenstein-Hawking entropy.Comment: 15 pages, 16 figures, 3D noncommutative black hole included as Sec 4, a version to appear in EPJ

Quantum Cooling Evaporation Process in Regular Black Holes

We investigate a universal behavior of thermodynamics and evaporation process for the regular black holes. We newly observe an important point where the temperature is maximum, the heat capacity is changed from negative infinity to positive infinity, and the free energy is minimum. Furthermore, this point separates the evaporation process into the early stage with negative heat capacity and the late stage with positive heat capacity. The latter represents the quantum cooling evaporation process. As a result, the whole evaporation process could be regarded as the inverse Hawking-Page phase transition.Comment: 11 pages, 3 figures, version to appear in Phys. Lett.

Thermodynamics and evaporation of the noncommutative black hole

We investigate the thermodynamics of the noncommutative black hole whose static picture is similar to that of the nonsingular black hole known as the de Sitter-Schwarzschild black hole. It turns out that the final remnant of extremal black hole is a thermodynamically stable object. We describe the evaporation process of this black hole by using the noncommutativity-corrected Vaidya metric. It is found that there exists a close relationship between thermodynamic approach and evaporation process.Comment: 16 pages, 6 figures, added references, to appear in JHE

Gravitational Collapse of the Shells with the Smeared Gravitational Source in Noncommutative Geometry

We study the formation of the (noncommutative) Schwarzschild black hole from collapsing shell {of the} generalized matters containing polytropic and Chaplygin gas. We show that this collapsing shell depending on various parameters forms either a black hole or a naked singular shell with the help of the pressure.Furthermore, by considering the smeared gravitational sources, we investigate the noncommutative black holes formation. Though this mild noncommutative correction of matters cannot ultimately resolve the emergence of the naked singularity, we show that in some parameter region the collapsing shell evolves to a noncommutative black hole before becoming a naked singular shell.Comment: 16 pages, LateX, 9 figures, Title changed in this published versio

Entropy of the Randall-Sundrum black brane world to all orders in the Planck length

We study the effects, to all orders in the Planck length from a generalized uncertainty principle (GUP), on the statistical entropy of massive scalar bulk fields in the Randall-Sundrum black brane world. We show that the Bekenstein-Hawking area law is not preserved, and contains small corrections terms proportional to the black hole inverse area.Comment: 19 pages, 1 figure. (v2): section 4 improve

Entropy of an extremal regular black hole

We introduce a magnetically charged extremal regular black hole in the coupled system of Einstein gravity and nonlinear electrodynamics. Its near horizon geometry is given by $AdS_2\times S^2$. It turns out that the entropy function approach does not automatically lead to a correct entropy of the Bekenstein-Hawking entropy. This contrasts to the case of the extremal Reissner-Norstr\"om black hole in the Einstein-Maxwell theory. We conclude that the entropy function approach does not work for a magnetically charged extremal regular black hole without singularity, because of the nonlinearity of the entropy function.Comment: 17 Pages, 4 figures, version to appear in Phys. Lett.