737 research outputs found
Fractal Structure of Loop Quantum Gravity
In this paper we have calculated the spectral dimension of loop quantum
gravity (LQG) using simple arguments coming from the area spectrum at different
length scales. We have obtained that the spectral dimension of the spatial
section runs from 2 to 3, across a 1.5 phase, when the energy of a probe scalar
field decrees from high to low energy. We have calculated the spectral
dimension of the space-time also using results from spin-foam models, obtaining
a 2-dimensional effective manifold at hight energy. Our result is consistent
with other two approach to non perturbative quantum gravity: causal dynamical
triangulation and asymptotic safety quantum gravity.Comment: 5 pages, 5 figure
Loop quantum black hole
In this paper we consider the Kantowski-Sachs space-time in Ashtekar
variables and the quantization of this space-time starting from the complete
loop quantum gravity theory. The Kanthowski-Sachs space-time coincides with the
Schwarzschild black hole solution inside the horizon. By studying this model we
can obtain information about the black hole singularity and about the dynamics
across the point r=0. We studied this space-time in ADM variables in two
previous papers where we showed that the classical black hole singularity
disappears in quantum theory. In this work we study the same model in Ashtekar
variables and we obtain a regular space-time inside the horizon region and that
the dynamics can be extend further the classical singularity.Comment: 12 pages, latex. We introduce and we calculate the spectrum of the
operator 1/|E
Mass Inflation in the Loop Black Hole
In classical general relativity the Cauchy horizon within a two-horizon black
hole is unstable via a phenomenon known as mass inflation, in which the mass
parameter (and the spacetime curvature) of the black hole diverges at the
Cauchy horizon. Here we study this effect for loop black holes -- quantum
gravitationally corrected black holes from loop quantum gravity -- whose
construction alleviates the singularity present in their classical
counterparts. We use a simplified model of mass inflation, which makes use of
the generalized DTR relation, to conclude that the Cauchy horizon of loop black
holes indeed results in a curvature singularity similar to that found in
classical black holes. The DTR relation is of particular utility in the loop
black hole because it does not directly rely upon Einstein's field equations.
We elucidate some of the interesting and counterintuitive properties of the
loop black hole, and corroborate our results using an alternate model of mass
inflation due to Ori.Comment: Latex 20 pages, 7 figure
Newtonian gravity as an entropic force: Towards a derivation of G
It has been suggested that the Newtonian gravitational force may emerge as an
entropic force from a holographic microscopic theory. In this framework, the
possibility is reconsidered that Newton's gravitational coupling constant G can
be derived from the fundamental constants of the underlying microscopic theory.Comment: 10 pages. v6: published versio
Background independence in a nutshell
We study how physical information can be extracted from a background
independent quantum system. We use an extremely simple `minimalist' system that
models a finite region of 3d euclidean quantum spacetime with a single
equilateral tetrahedron. We show that the physical information can be expressed
as a boundary amplitude. We illustrate how the notions of "evolution" in a
boundary proper-time and "vacuum" can be extracted from the background
independent dynamics.Comment: 19 pages, 19 figure
Gravitational collapse in loop quantum gravity
In this paper we study the gravitational collapse in loop quantum gravity. We
consider the space-time region inside the Schwarzschild black hole event
horizon and we divide this region in two parts, the first one where the matter
(dust matter) is localized and the other (outside) where the metric is
Kantowski-Sachs type. We calculate the state solving Hamiltonian constraint and
we obtain a set of three difference equations that give a regular and natural
evolution beyond the classical singularity point in "r=0" localized.Comment: 16 pages, 2 figure
Sub-Planckian black holes and the Generalized Uncertainty Principle
The Black Hole Uncertainty Principle correspondence suggests that there could
exist black holes with mass beneath the Planck scale but radius of order the
Compton scale rather than Schwarzschild scale. We present a modified, self-dual
Schwarzschild-like metric that reproduces desirable aspects of a variety of
disparate models in the sub-Planckian limit, while remaining Schwarzschild in
the large mass limit. The self-dual nature of this solution under naturally implies a Generalized Uncertainty Principle
with the linear form . We also
demonstrate a natural dimensional reduction feature, in that the gravitational
radius and thermodynamics of sub-Planckian objects resemble that of -D
gravity. The temperature of sub-Planckian black holes scales as rather than
but the evaporation of those smaller than g is suppressed by
the cosmic background radiation. This suggests that relics of this mass could
provide the dark matter.Comment: 12 pages, 9 figures, version published in J. High En. Phy
The Hawking-Page crossover in noncommutative anti-deSitter space
We study the problem of a Schwarzschild-anti-deSitter black hole in a
noncommutative geometry framework, thought to be an effective description of
quantum-gravitational spacetime. As a first step we derive the noncommutative
geometry inspired Schwarzschild-anti-deSitter solution. After studying the
horizon structure, we find that the curvature singularity is smeared out by the
noncommutative fluctuations. On the thermodynamics side, we show that the black
hole temperature, instead of a divergent behavior at small scales, admits a
maximum value. This fact implies an extension of the Hawking-Page transition
into a van der Waals-like phase diagram, with a critical point at a critical
cosmological constant size in Plank units and a smooth crossover thereafter. We
speculate that, in the gauge-string dictionary, this corresponds to the
confinement "critical point" in number of colors at finite number of flavors, a
highly non-trivial parameter that can be determined through lattice
simulations.Comment: 24 pages, 6 figure, 1 table, version matching that published on JHE
Time Evolution of Entropy in Gravitational Collapse
We study the time evolution of the entropy of a collapsing spherical domain
wall, from the point of view of an asymptotic observer, by investigating the
entropy of the entire system (i.e. domain wall and radiation) and induced
radiation alone during the collapse. By taking the difference, we find the
entropy of the collapsing domain wall, since this is the object which will form
a black hole. We find that for large values of time (times larger than
), the entropy of the collapsing domain wall is a constant,
which is of the same order as the Bekenstein-Hawking entropy.Comment: 9 pages, 6 figure
- …