386 research outputs found
Noncommutative nonsingular black holes
Adopting noncommutative spacetime coordinates, we determined a new solution
of Einstein equations for a static, spherically symmetric matter source. The
limitations of the conventional Schwarzschild solution, due to curvature
singularities, are overcome. As a result, the line element is endowed of a
regular DeSitter core at the origin and of two horizons even in the considered
case of electrically neutral, nonrotating matter. Regarding the Hawking
evaporation process, the intriguing new feature is that the black hole is
allowed to reach only a finite maximum temperature, before cooling down to an
absolute zero extremal state. As a consequence the quantum back reaction is
negligible.Comment: 10 pages, 2 figures, to appear in Proceedings to the 8th Workshop
`What Comes Beyond the Standard Model', July 19-29, 2005, Bled, Slovenia,
edited by C.D. Froggatt (Glasgow U.), N. Mankoc Borstnik (Ljubljana U.) and
H.B. Nielsen (Bohr Inst.
Mini-review on mini-black holes from the mini-Big Bang
We review the basic ideas about man-made quantum mechanical black holes. We
start by an overview of the proposed attempts to circumvent the hierarchy
problem. We study the phenomenological implications of a strong gravity regime
at the terascale and we focus on the issue of microscopic black holes. We
provide the experimental bounds on relevant quantities as they emerge from
major ongoing experiments. The experimental results exclude the production of
black holes in collisions up to 8 TeV. We provide some possible explanations of
such negative results in view of forthcoming investigations.Comment: 7 pages, 5 figures, paper based on the talk given at
STARS2013/SMFNS2013, Havana/Varadero, Cuba, 4-10 May 2013, submitted for a
special issue of Astronomische Nachrichten; v2 additional references and
comment
Holographic screens in ultraviolet self-complete quantum gravity
In this paper we study the geometry and the thermodynamics of a holographic
screen in the framework of the ultraviolet self-complete quantum gravity. To
achieve this goal we construct a new static, neutral, non-rotating black hole
metric, whose outer (event) horizon coincides with the surface of the screen.
The space-time admits an extremal configuration corresponding to the minimal
holographic screen and having both mass and radius equalling the Planck units.
We identify this object as the space-time fundamental building block, whose
interior is physically unaccessible and cannot be probed even during the
Hawking evaporation terminal phase. In agreement with the holographic
principle, relevant processes take place on the screen surface. The area
quantization leads to a discrete mass spectrum. An analysis of the entropy
shows that the minimal holographic screen can store only one byte of
information while in the thermodynamic limit the area law is corrected by a
logarithmic term.Comment: 18 pages, 4 figures; v2 additional references; v3 shortened version
in press as invited contribution to "Black hole Physics'', special issue of
Advances of High Energy Physics edited by X. Zeng, C. Corda and D. Che
Theory of stochastic transitions in area preserving maps
A famous aspect of discrete dynamical systems defined by area-preserving maps
is the physical interpretation of stochastic transitions occurring locally
which manifest themselves through the destruction of invariant KAM curves and
the local or global onset of chaos. Despite numerous previous investigations
(see in particular Chirikov, Greene, Percival, Escande and Doveil and MacKay)
based on different approaches, several aspects of the phenomenon still escape a
complete understanding and a rigorous description. In particular Greene's
approach is based on several conjectures, one of which is that the stochastic
transition leading to the destruction of the last KAM curve in the standard map
is due the linear destabilization of the elliptic points belonging to a
peculiar family of invariants sets {I(m,n)}
(rational iterates) having rational winding numbers and associated to the
last KAM curve. Purpose of this work is to analyze the nonlinear phenomena
leading to the stochastic transition in the standard map and their effect on
the destabilization of the invariant sets associated to the KAM curves,
leading, ultimately, to the destruction of the KAM curves themselves.Comment: 6 pages, 1 figure. Contributed to the Proceedings of the 24th
International Symposium on Rarefied Gas Dynamics, July 10-16, 2004 Porto
Giardino Monopoli (Bari), Ital
Un-spectral dimension and quantum spacetime phases
In this Letter, we propose a new scenario emerging from the conjectured
presence of a minimal length in the spacetime fabric, on the one side,
and the existence of a new scale invariant, continuous mass spectrum, of
un-particles on the other side. We introduce the concept of \textit{un-spectral
dimension} of a -dimensional, euclidean (quantum) spacetime,
as the spectral dimension measured by an "un-particle" probe. We find a general
expression for the un-spectral dimension labelling different
spacetime phases: a semi-classical phase, where ordinary spectral dimension
gets contribution from the scaling dimension of the un-particle probe ; a
critical "Planckian phase", where four-dimensional spacetime can be effectively
considered two-dimensional when ; a "Trans-Planckian phase", which is
accessible to un-particle probes only, where spacetime as we currently
understand it looses its physical meaning.Comment: 5 pages, 1 figure, version matching that published by Physics Letters
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
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