755 research outputs found
Astrophysical Production of Microscopic Black Holes in a Low Planck-scale World
In the framework of brane-world models lowering the Planck scale to the TeV
range, it has recently been pointed out that small black holes could be formed
at particle colliders or by neutrinos interactions in the atmosphere. This
article aims at reviewing other places and epochs where microscopic black holes
could be formed : the interstellar medium and the early Universe. The related
decay channels and the propagation of the emitted particles are studied to
conclude that, in spite of the large creation rate for such black holes, the
amount of produced particles do not conflict with experimental data. This
shows, from the astronomical viewpoint, that models with large extra dimensions
making the gravity scale much lower are compatible with observations.Comment: To appear in Ap
World-making with extended gravity black holes for cosmic natural selection in the multiverse scenario
Physics is facing contingency. Not only in facts but also in laws (the
frontier becoming extremely narrow). Cosmic natural selection is a tantalizing
idea to explain the apparently highly improbable structure of our Universe. In
this brief note I will study the creation of Universes by black holes in
-string inspired- higher order curvature gravity.Comment: 5 pages, 1 figure. Proceedings of the Eleventh Marcel Grossmann
Meeting on General Relativity, edited by H. Kleinert, R.T. Jantzen and R.
Ruffini, World Scientific, Singapore, 200
Holonomy corrections to the cosmological primordial tensor power spectrum
Loop quantum gravity is one of the leading candidate theory to
non-perturbatively quantize gravity. In this framework, holonomy corrections to
the equation of propagation of gravitons in a FLRW background have been
derived. We investigate the consequences of those corrections on the tensor
power spectrum in de-Sitter and slow-roll inflations, for n=-1/2. Depending on
the value of the Barbero-Immirzi parameter, several observational features
could be expected.Comment: 5 pages, Proc. of the 43rd Rencontres de Moriond "Cosmology 2008
Could the next generation of cosmology experiments exclude supergravity?
Gravitinos are expected to be produced in any local supersymmetric model.
Using their abundance prediction as a function of the reheating energy scale,
it is argued that the next generation of Cosmic Microwave Background
experiments could exclude supergravity or strongly favor "thermal-like"
inflation models if B mode polarized radiation were detected. Galactic
cosmic--ray production by evaporating primordial black holes is also
investigated as a way of constraining the Hubble mass at the end of inflation.
Subsequent limits on the gravitino mass and on the related grand unification
parameters are derived.Comment: 8 pages, 5 figures, published version with minor changes, results
unchange
Internal structure of a Maxwell-Gauss-Bonnet black hole
The influence of the Maxwell field on a static, asymptotically flat and
spherically-symmetric Gauss-Bonnet black hole is considered. Numerical
computations suggest that if the charge increases beyond a critical value, the
inner determinant singularity is replaced by an inner singular horizon.Comment: 5 pages, 5 figures, published version with minor change
Very high energy gamma-rays and the Hubble parameter
A new method, based on the absorption of very high-energy gamma-rays by the
cosmic infrared background, is proposed to constrain the value of the Hubble
constant. As this value is both fundamental for cosmology and still not very
well measured, it is worth developing such alternative methods. Our lower limit
at the 68% confidence level is H0 > 74 km/s/Mpc, leading, when combined with
the HST results, to H0 ~ 76 km/s/Mpc. Interestingly, this value, which is
significantly higher than the usually considered one, is in exact agreement
with other independent approaches based on baryonic acoustic oscillations and
X-ray measurements. Forthcoming data from the experiments HESS-2 and CTA should
help improving those results. Finally, we briefly mention a plausible
correlation between absorption by the extragalactic background light and the
absence of observation of gamma-ray bursts (GRBs) at very high energies.Comment: Proc. of the 12th Marcel Grossmann meeting on general relativity. 3
pages, 1 figur
Phenomenology of black hole evaporation with a cosmological constant
In this brief note, we investigate some possible experimental consequences of
the de-Sitter or Anti-de-Sitter background spacetime structure for
d-dimensional evaporating black holes. Possible observational signatures in
Large Hadron Collider (LHC) events are considered in the framework of the
Arkani-Hamed-Dimopoulos-Dvali (ADD) braneworld model. Lower bounds on the value
of the bulk cosmological constant required to produce visible effects are
derived thanks to a dynamical Monte-Carlo simulation. This preliminary study
has to be refined by the accurate computation of the greybody factors. It opens
a new way to investigate the structure of non-asymptotically flat
higher-dimensional spacetimes.Comment: Proceedings of the HEP2005 conference. Related greybody factors for
evaporating black holes available at : http://lpsc.in2p3.fr/ams/greybody
Observational issues in loop quantum cosmology
Quantum gravity is sometimes considered as a kind of metaphysical
speculation. In this review, we show that, although still extremely difficult
to reach, observational signatures can in fact be expected. The early universe
is an invaluable laboratory to probe "Planck scale physics". Focusing on Loop
Quantum Gravity as one of the best candidate for a non-perturbative and
background-independant quantization of gravity, we detail some expected
features.Comment: 75 pages, invited topical review for Classical and Quantum Gravit
Baryonic acoustic oscillations simulations for the Large Synoptic Survey Telescope (LSST)
The baryonic acoustic oscillations are features in the spatial distribution
of the galaxies which, if observed at different epochs, probe the nature of the
dark energy. In order to be able to measure the parameters of the dark energy
equation of state to high precision, a huge sample of galaxies has to be used.
The Large Synoptic Survey Telescope will survey the optical sky with 6 filters
from 300nm and 1100nm, such that a catalog of galaxies with photometric
redshifts will be available for dark energy studies. In this article, we will
give a rough estimate of the impact of the photometric redshift uncertainties
on the computation of the dark energy parameter through the reconstruction of
the BAO scale from a simulated photometric catalog.Comment: 4 pages, 2 figures, 10th Rencontres de Blois proceedin
Semiclassical scalar propagators in curved backgrounds: formalism and ambiguities
The phenomenology of quantum systems in curved space-times is among the most
fascinating fields of physics, allowing --often at the gedankenexperiment
level-- constraints on tentative theories of quantum gravity. Determining the
dynamics of fields in curved backgrounds remains however a complicated task
because of the highly intricate partial differential equations involved,
especially when the space metric exhibits no symmetry. In this article, we
provide --in a pedagogical way-- a general formalism to determine this dynamics
at the semiclassical order. To this purpose, a generic expression for the
semiclassical propagator is computed and the equation of motion for the
probability four-current is derived. Those results underline a direct analogy
between the computation of the propagator in general relativistic quantum
mechanics and the computation of the propagator for stationary systems in
non-relativistic quantum mechanics. A possible application of this formalism to
curvature-induced quantum interferences is also discussed.Comment: New materials on gravitationally-induced quantum interferences has
been adde
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