The primordial spectrum of cosmological tensor perturbations is considered as a possible probe of quantum gravity effects. Together with string theory, loop quantum gravity is one of the most ...promising frameworks to study quantum effects in the early universe. We show that the associated corrections should modify the potential seen by gravitational waves during the inflationary amplification. The resulting power spectrum should exhibit a characteristic tilt. This opens a new window for cosmological tests of quantum gravity.
The primordial universe can be used as a laboratory to set constraints on quantum gravity. In the framework of Loop Quantum Cosmology, we show that such a proposal for quantum gravity, not only ...solves for the big bang singularity issue, but also naturally generates inflation. Thanks to a quantitative computation of the amount of gravity waves produced in the loopy early universe, we show that future cosmological data on the polarized anisotropies of the Cosmic Microwave Background can be used to probe LQC model of the universe.
Magnetized plasmas within haloes of galaxies leave their footprint on the polarized anisotropies of the cosmic microwave background. The two dominant effects of astrophysical haloes are Faraday ...rotation, which generates rotation of the plane of linear polarization, and Faraday conversion, which induces a leakage from linear polarization to circular polarization. We revisit these sources of secondary anisotropies by computing the angular power spectra of the Faraday rotation angle and the Faraday conversion rate by the large-scale structures. To this end, we use the halo model and we pay special attention to the impact of magnetic field projections. Assuming magnetic fields of haloes to be uncorrelated, we found a vanishing two-halo term, and angular power spectra peaking at multipoles ℓ ∼ 104. The Faraday rotation angle is dominated by the contribution of thermal electrons. For the Faraday conversion rate, we found that both thermal electrons and relativistic, non-thermal electrons contribute equally in the most optimistic case for the density and Lorentz factor of relativistic electrons, while in more pessimistic cases the thermal electrons give the dominant contribution. Assuming the magnetic field to be independent of the halo mass, the angular power spectra for both effects roughly scale with the amplitude of matter perturbations as ∼σ38 ∼ σ 8 3 $ {\sim}\sigma_{8}^{3} $ , and with a very mild dependence with the density of cold dark matter. Introducing a dependence of the magnetic field strength with the halo mass leads to an increase of the scaling at large angular scales (above a degree) with the amplitude of matter fluctuations up to ∼σ9.58 ∼ σ 8 9.5 $ {\sim}\sigma_{8}^{9.5} $ for Faraday rotation and ∼σ158 ∼ σ 8 15 $ {\sim}\sigma_{8}^{15} $ for Faraday conversion for a magnetic field strength scaling linearly with the halo mass. Introducing higher values of the magnetic field for galaxies, as compared to clusters, instead leads to a decrease of such a scaling at arcminute scales down to ∼σ0.98 ∼ σ 8 0.9 $ {\sim}\sigma_{8}^{0.9} $ for Faraday rotation.
The estimation of the B-mode angular power spectrum of polarized anisotropies of the cosmic microwave background is a key step towards a full exploitation of the scientific potential of this probe. ...In the context of pseudo-spectrum methods the major challenge is related to a contamination of the B-mode spectrum estimate with the residual power of the much larger E-mode. This so-called E-to-B leakage is unavoidably present whenever only an incomplete sky map is available, as is the case for any realistic observation. We find that although all these methods allow us to reduce significantly the level of the E-to-B leakage, it is the method of Smith that at the same time ensures the smallest error bars in all experimental configurations studied here, owing to the fact that it permits straightforwardly an optimization of the sky apodization of the polarization maps used for the estimation. For a satellite-like experiment, this method enables a detection of the B-mode power spectrum at large angular scales but only after appropriate binning. The method of Zhao and Baskaran is a close runner-up in the case of a nearly full-sky coverage.
This Letter aims at showing that the observation of evaporating black holes should allow the usual Hawking behavior to be distinguished from loop quantum gravity (LQG) expectations. We present a full ...Monte Carlo simulation of the evaporation in LQG and statistical tests that discriminate between competing models. We conclude that contrarily to what was commonly thought, the discreteness of the area in LQG leads to characteristic features that qualify evaporating black holes as objects that could reveal quantum gravity footprints.
Context. The measurement of the anisotropies in the cosmic infrared background (CIB) is a powerful means of studying the evolution of galaxies and large-scale structures. These anisotropies have been ...measured by a number of experiments, from the far-infrared (AKARI 90 μm) to the millimeter (Planck and the South Pole Telescope at ~2 mm). One of the main impediments to an accurate measurement on large scales ( ≲ 1 degree) is the contamination of the foreground signal by Galactic dust emission. Aims. Our goal is to show that we can remove the Galactic cirrus contamination using Hi data, and thus accurately measure the clustering of starburst galaxies in the CIB. Methods. We use observations of the so-called extragalactic ELAIS N1 field at far-infrared (100 and 160 μm) and radio (21 cm) wavelengths. We compute the correlation between dust emission, traced by far-infrared observations, and Hi gas traced by 21 cm observations, and derive dust emissivities that enable us to subtract the cirrus emission from the far-infrared maps. We then derive the power spectrum of the CIB anisotropies, as well as its mean level at 100 μm and 160 μm. Results. We compute dust emissivities for each of the Hi-velocity components (local, intermediate, and high velocity). Using IRIS/IRAS data at 100 μm, we demonstrate that we can use the measured emissivities to determine and remove the cirrus contribution to the power spectrum of the CIB on large angular scales where the cirrus contribution dominates. We then apply this method to Spitzer/MIPS data for 160 μm. We measure correlated anisotropies at 160 μm, and for the first time at 100 μm. We also combine the Hi data and Spitzer total power mode absolute measurements to determine the CIB mean level at 160 μm. We find B160 = 0.77 ± 0.04 ± 0.12 MJy/sr, where the first error is statistical and the second one systematic. Combining this measurement with the B100/B160 color of the correlated anisotropies, we also derive the CIB mean at 100 μm, B100 = 0.24 ± 0.08 ± 0.04 MJy/sr. This measurement is in line with values obtained with recent models of infrared galaxy evolution and Herschel/PACS data, but is much smaller than the previous DIRBE measurements. In contrast to Matsuura and collaborators, we do not find any evidence of a new galaxy population at high redshift or unknown diffuse emission. Part of this discrepancy is likely to be explained by their use of an incorrect template for the Galactic cirrus emission. Conclusions. The use of high-angular resolution Hi data is mandatory to accurately differentiate the cirrus from the CIB emission. The 100 μm IRAS map (and thus the map developed by Schlegel and collaborators) in such extragalactic fields is highly contaminated by the CIB anisotropies and hence cannot be used as a Galactic cirrus tracer.
Quantum bound states around black holes Grain, J.; Barrau, A.
European physical journal. C, Particles and fields,
02/2008, Letnik:
53, Številka:
4
Journal Article
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Quantum mechanics in the vicinity of black holes is a fascinating field of theoretical physics. It involves both general relativity and particle physics, opening new eras to establish the principles ...of unified theories. In this article, we show that quantum bound states with no classical equivalent – as can easily be seen at the dominant monopolar order – should be formed around black holes for massive scalar particles. We qualitatively investigate some important physical consequences, in particular for the Hawking evaporation mechanism and the associated greybody factors.
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