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

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

Comparison of primordial tensor power spectra from the deformed algebra and dressed metric approaches in loop quantum cosmology

Loop quantum cosmology tries to capture the main ideas of loop quantum gravity and to apply them to the Universe as a whole. Two main approaches within this framework have been considered to date for the study of cosmological perturbations: the dressed metric approach and the deformed algebra approach. They both have advantages and drawbacks. In this article, we accurately compare their predictions. In particular, we compute the associated primordial tensor power spectra. We show -- numerically and analytically -- that the large scale behavior is similar for both approaches and compatible with the usual prediction of general relativity. The small scale behavior is, the other way round, drastically different. Most importantly, we show that in a range of wavenumbers explicitly calculated, both approaches do agree on predictions that, in addition, differ from standard general relativity and do not depend on unknown parameters. These features of the power spectrum at intermediate scales might constitute a universal loop quantum cosmology prediction that can hopefully lead to observational tests and constraints. We also present a complete analytical study of the background evolution for the bouncing universe that can be used for other purposes.Comment: 15 pages, 7 figure

Exact Results for Evaporating Black Holes in Curvature-Squared Lovelock Gravity: Gauss-Bonnet Greybody Factors

Lovelock gravity is an important extension of General Relativity that provides a promising framework to study curvature corrections to the Einstein action, while avoiding ghosts and keeping second order field equations. This paper derives the greybody factors for D-dimensional black holes arising in a theory with a Gauss-Bonnet curvature-squared term. These factors describe the non-trivial coupling between black holes and quantum fields during the evaporation process: they can be used both from a theoretical viewpoint to investigate the intricate spacetime structure around such a black hole, and for phenomenological purposes in the framework of braneworld models with a low Planck scale. We derive exact spectra for the emission of scalar, fermion and gauge fields emitted on the brane, and for scalar fields emitted in the bulk, and demonstrate how the Gauss-Bonnet term can change the bulk-to-brane emission rates ratio in favour of the bulk channel in particular frequency regimes.Comment: 29 pages, Latex file, 11 figures, Data files (greybody factors) available at http://lpsc.in2p3.fr/ams/greybody/, typos corrected, references added, version to appear in Phys. Rev.

Consistency of holonomy-corrected scalar, vector and tensor perturbations in Loop Quantum Cosmology

Loop Quantum Cosmology yields two kinds of quantum corrections to the effective equations of motion for cosmological perturbations. Here we focus on the holonomy kind and we study the problem of the closure of the resulting algebra of constraints. Up to now, tensor, vector and scalar perturbations were studied independently, leading to different algebras of constraints. The structures of the related algebras were imposed by the requirement of anomaly freedom. In this article we show that the algebra can be modified by a very simple quantum correction, holding for all types of perturbations. This demonstrates the consistency of the theory and shows that lessons from the study of scalar perturbations should be taken into account when studying tensor modes. The Mukhanov-Sasaki equations of motion are similarly modified by a simple term.Comment: 5 page

Kerr-Gauss-Bonnet Black Holes: An Analytical Approximation

Gauss-Bonnet gravity provides one of the most promising frameworks to study curvature corrections to the Einstein action in supersymmetric string theories, while avoiding ghosts and keeping second order field equations. Although Schwarzschild-type solutions for Gauss-Bonnet black holes have been known for long, the Kerr-Gauss-Bonnet metric is missing. In this paper, a five dimensional Gauss-Bonnet approximation is analytically derived for spinning black holes and the related thermodynamical properties are briefly outlined.Comment: 5 pages, 1 figur

Targeting the fatty acid transport proteins (FATP) to understand the mechanisms linking fatty acid transport to metabolism

One principal process driving fatty acid transport is vectorial acylation, where fatty acids traverse the membrane concomitant with activation to CoA thioesters. Current evidence is consistent with the proposal that specific fatty acid transport (FATP) isoforms alone or in concert with specific long chain acyl CoA synthetase (Acsl) isoforms function to drive this energy-dependent process. Understanding the details of vectorial acylation is of particular importance as disturbances in lipid metabolism many times leads to elevated levels of circulating free fatty acids, which in turn increases fatty acid internalization and ectopic accumulation of triglycerides. This is associated with changes in fatty acid oxidation rates, accumulation of reactive oxygen species, the synthesis of ceramide and ER stress. The correlation between chronically elevated plasma free fatty acids and triglycerides with the development of obesity, insulin resistance and cardiovascular disease has led to the hypothesis that decreases in pancreatic insulin production, cardiac failure, arrhythmias, and hypertrophy are due to aberrant accumulation of lipids in these tissues. To this end, a detailed understanding of how fatty acids traverse the plasma membrane, become activated and trafficked into downstream metabolic pools and the precise roles provided by the different FATP and Acsl isoforms are especially important questions. We review our current understanding of vectorial acylation and the contributions by specific FATP and Acsl isoforms and the identification of small molecule inhibitors from high throughput screens that inhibit this process and thus provide new insights into the underlying mechanistic basis of this process

Targeting the fatty acid transport proteins (FATP) to understand the mechanisms linking fatty acid transport to metabolism

One principal process driving fatty acid transport is vectorial acylation, where fatty acids traverse the membrane concomitant with activation to CoA thioesters. Current evidence is consistent with the proposal that specific fatty acid transport (FATP) isoforms alone or in concert with specific long chain acyl CoA synthetase (Acsl) isoforms function to drive this energy-dependent process. Understanding the details of vectorial acylation is of particular importance as disturbances in lipid metabolism many times leads to elevated levels of circulating free fatty acids, which in turn increases fatty acid internalization and ectopic accumulation of triglycerides. This is associated with changes in fatty acid oxidation rates, accumulation of reactive oxygen species, the synthesis of ceramide and ER stress. The correlation between chronically elevated plasma free fatty acids and triglycerides with the development of obesity, insulin resistance and cardiovascular disease has led to the hypothesis that decreases in pancreatic insulin production, cardiac failure, arrhythmias, and hypertrophy are due to aberrant accumulation of lipids in these tissues. To this end, a detailed understanding of how fatty acids traverse the plasma membrane, become activated and trafficked into downstream metabolic pools and the precise roles provided by the different FATP and Acsl isoforms are especially important questions. We review our current understanding of vectorial acylation and the contributions by specific FATP and Acsl isoforms and the identification of small molecule inhibitors from high throughput screens that inhibit this process and thus provide new insights into the underlying mechanistic basis of this process

Bulk and Brane Decay of a (4+n)-Dimensional Schwarzschild-De-Sitter Black Hole: Scalar Radiation

In this paper, we extend the idea that the spectrum of Hawking radiation can reveal valuable information on a number of parameters that characterize a particular black hole background - such as the dimensionality of spacetime and the value of coupling constants - to gain information on another important aspect: the curvature of spacetime. We investigate the emission of Hawking radiation from a D-dimensional Schwarzschild-de-Sitter black hole emitted in the form of scalar fields, and employ both analytical and numerical techniques to calculate greybody factors and differential energy emission rates on the brane and in the bulk. The energy emission rate of the black hole is significantly enhanced in the high-energy regime with the number of spacelike dimensions. On the other hand, in the low-energy part of the spectrum, it is the cosmological constant that leaves a clear footprint, through a characteristic, constant emission rate of ultrasoft quanta determined by the values of black hole and cosmological horizons. Our results are applicable to "small" black holes arising in theories with an arbitrary number and size of extra dimensions, as well as to pure 4-dimensional primordial black holes, embedded in a de Sitter spacetime.Comment: 31 pages, latex file, data files available at http://lpsc.in2p3.fr/ams/greybody/ some clarifying comments and references added, typos corrected, version to appear in Phys. Rev.

Evolution of Primordial Black Hole Mass Spectrum in Brans-Dicke Theory

We investigate the evolution of primordial black hole mass spectrum by including both accretion of radiation and Hawking evaporation within Brans-Dicke cosmology in radiation, matter and vacuum-dominated eras. We also consider the effect of evaporation of primordial black holes on the expansion dynamics of the universe. The analytic solutions describing the energy density of the black holes in equilibrium with radiation are presented. We demonstrate that these solutions act as attractors for the system ensuring stability for both linear and nonlinear situations. We show, however, that inclusion of accretion of radiation delays the onset of this equilibrium in all radiation, matter and vacuum-dominated eras.Comment: 18 pages, one figur