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

Loop Quantum Cosmology corrections on gravity waves produced during primordial inflation

Loop Quantum Gravity (L.Q.G.) is one of the two most promising tentative theory for a quantum description of gravity. When applied to the entire universe, the so-called Loop Quantum Cosmology (L.Q.C.) framework offers microscopical models of the very early stages of the cosmological history, potentially solving the initial singularity problem via bouncing solutions or setting the universe in the appropriate initial conditions for inflation to start, via a phase of super-inflation. More interestingly, L.Q.C. could leave a footprint on cosmological observables such as the Cosmic Microwave Background (CMB) anisotropies. Focusing on the modified dispersion relation when holonomy and inverse-volume corrections arising from the L.Q.C. framework are considered, it is shown that primordial gravity waves generated during inflation are affected by quantum corrections. Depending on the type of corrections, the primordial tensor power spectrum is either suppressed or boosted at large length scales, and strongly departs from the power-law behavior expected in the standard scenario.Comment: to be published in the AIP Proceedings of the 'Invisible Universe International Conference', UNESCO-Paris, June 29-July 3, 2009; 9 pp., 4 Fig

The perturbed universe in the deformed algebra approach of Loop Quantum Cosmology

Loop quantum cosmology is a tentative approach to model the universe down to the Planck era where quantum gravity settings are needed. The quantization of the universe as a dynamical space-time is inspired by Loop Quantum Gravity ideas. In addition, loop quantum cosmology could bridge contact with astronomical observations, and thus potentially investigate quantum cosmology modellings in the light of observations. To do so however, modelling both the background evolution and its perturbations is needed. The latter describe cosmic inhomogeneities that are the main cosmological observables. In this context, we present the so-called deformed algebra approach implementing the quantum corrections to the perturbed universe at an effective level by taking great care of gauge issues. We particularly highlight that in this framework, the algebra of hypersurface deformation receives quantum corrections, and we discuss their meaning. The primordial power spectra of scalar and tensor inhomogeneities are then presented, assuming initial conditions are set in the contracting phase preceding the quantum bounce and the well-known expanding phase of the cosmic history. These spectra are subsequently propagated to angular power spectra of the anisotropies of the cosmic microwave background. It is then shown that regardless of the choice for the initial conditions inside the effective approach for the background evolution (except that they are set in the contracting phase), the predicted angular power spectra of the polarized B-modes exceed the upper bound currently set by observations. The exclusion of this specific version of loop quantum cosmology establishes the falsifiability of the approach, though one shall not conclude here that either loop quantum cosmology or loop quantum gravity is excluded.Comment: Invited paper for a special issue of IJMPD on Loop Quantum Cosmolog

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

Transgénicos : ¿20 años alimentando o engañando al mundo?

Persisten los mitos y crecen las mentiras, vivamente alimentadas por la industria, sobre los supuestos beneficios de los cultivos transgénicos. Estos engaños se pueden resumir en cinco: que alimentarán al mundo, que producen más, que eliminarán el uso de los agroquímicos, que coexisten armoniosamente con otros cultivos y que son absolutamente seguros para el medio ambiente y la salud. Desmontar el engaño es sencillo, sólo se trata de echar una mirada, desapasionada y objetiva, a lo que de verdad está pasando en el campo, con datos de la propia industria. La conclusión, después de veinte años de siembra transgénica comercial, es clara: ninguna de las promesas se está cumpliendo, más bien todo lo contrario. Veamos los cinco puntos uno por uno

¿Quién hay detrás de la Agricultura Climáticamente Inteligente?

Esto de la Agricultura Climáticamente Inteligente (ACI) se ha oído sin cesar en los diferentes espacios de la Conferencia del Clima de París, COP21, como una palabra mágica que puede resolver parte del problema de las emisiones que contribuyen al cambio climático. Pero, como ya advertíamos antes de la cumbre, tras este antifaz tenemos otra vez a la agroindustria buscando alcanzar sus particulares objetivos

Primordial tensor power spectrum in holonomy corrected Omega-LQC

The holonomy correction is one of the main terms arising when implementing loop quantum gravity ideas at an effective level in cosmology. The recent construction of an anomaly free algebra has shown that the formalism used, up to now, to derive the primordial spectrum of fluctuations was not correct. This article aims at computing the tensor spectrum in a fully consistent way within this deformed and closed algebra.Comment: 5 pages, 6 figures, accepted by Phys. Rev.

Observational Exclusion of a Consistent Quantum Cosmology Scenario

It is often argued that inflation erases all the information about what took place before it started. Quantum gravity, relevant in the Planck era, seems therefore mostly impossible to probe with cosmological observations. In general, only very ad hoc scenarios or hyper fine-tuned initial conditions can lead to observationally testable theories. Here we consider a well-defined and well motivated candidate quantum cosmology model that predicts inflation. Using the most recent observational constraints on the cosmic microwave background B modes, we show that the model is excluded for all its parameter space, without any tuning. Some important consequences are drawn for the deformed algebra approach to loop quantum cosmology. We emphasize that neither loop quantum cosmology in general nor loop quantum gravity are disfavored by this study but their falsifiability is established.Comment: 5 pages, 2 figur