Aurelien Barrau

Antiprotons from Spallations of Cosmic Rays on Interstellar Matter

Cosmic-ray antiprotons provide an important probe for the study of Galactic dark matter, as they could be produced by neutralino annihilations, primordial black holes evaporations, or other exotic sources. On the other hand, antiprotons are anyway produced by standard nuclear reactions of cosmic-ray nuclei on interstellar matter (spallations), which are known to occur in the Galaxy. This process is responsible for a background flux that must be carefully determined to estimate the detectability of an hypothetical exotic signal. In this paper we provide a new evaluation of the interstellar cosmic antiproton flux that is fully consistent with cosmic-ray nuclei in the framework of a two-zone diffusion model. We also study and conservatively quantify all possible sources of uncertainty that may affect that antiproton flux. In particular, the primary cosmic rays are by now so well measured that the corresponding error is removed. Uncertainties related to propagation are shown to range between 10% and 25%, depending on which part of the spectrum is considered.Cosmic ray antiprotons provide an important probe for the study of the galactic Dark Matter, as they could be produced by exotic sources. On the other hand, antiprotons are anyway produced by standard nuclear reactions of cosmic ray nuclei on interstellar matter. This process is responsible for a background flux that must be carefully determined to estimate the detectability of an hypothetical exotic signal. Estimates of this background suffer from potential uncertainties of various origins. The propagation of cosmic antiprotons depends on several physical characteristics of the Galaxy which are poorly known. Antiprotons are created from cosmic protons and helium nuclei whose fluxes were not measured with great accuracy until very recently. Calculations of antiproton fluxes make use of nuclear physics models with their own shortcomings and uncertainties. The goal of this paper is to give a new evaluation of the cosmic antiproton flux along with the associated uncertainties. The propagation parameters were tightly constrained in Maurin et al. 2001 by an analysis of cosmic ray nuclei data in the framework of a two-zone diffusion model and we apply these parameters to the propagation of antiprotons. We use the recently published data on proton and helion fluxes, and we find that this particular source of uncertainty has become negligible. The Monte Carlo program DTUNUC was used to carefully examine nuclear reactions. We find that all the cosmic antiproton fluxes naturally coming out of the calculation are fully compatible with experimental data. Uncertainties in this flux have been strongly reduced. Those related to propagation are less than 25%. All other possible sources of uncertainty have also been studied.

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.

Flux of light antimatter nuclei near earth, induced by Cosmic Rays in the Galaxy and in the atmosphere.

The fluxes of light antinuclei A� 4 induced near earth by Cosmic Ray interactions with the interstellar matter in the Galaxy and with the Earth atmosphere are calculated in a phenomenological framework. The hadronic production cross section for antinucleons is based on a recent parametrization of a wide set of accelerator data. The production of light nuclei is calculated using coalescence models. For the standard coalescence model, the coalescence radius is fitted to the available experimental data. The non annihilating inelastic scattering process for the antideuterons is discussed and taken into account for the first time via a more realistic procedure than used so far for antiprotons. Antiprotons in Cosmic Rays (CR) have been extensively studied both experimentally and theoretically over the last few decades, with the general purpose of measuring their flux and understanding their origin. It is now generally agreed that the dominant part of the ¯ p CR spectrum is a secondary flux originating from the hadronic production induced by CRs on the interstellar (IS) medium (ISM). This agreement is grounded on the ability of the calculations based on this assumption to reproduce the data. Recently some new prospects have been outlined, strengthening the motivations for the study of the ¯ p flux [1], and extending the interest for CR antimatter to other light antinuclei, antideuterons ¯ d in particular, with the emergence of new astrophysical issues. The ¯ p and ¯ d production in neutralino annihilation has been considered as a possible signature for the Dark Matter constituents in the universe [2]. Antiprotons and antideuterons have also been considered as evaporation products of primordial black holes (PBH) and their flux at earth calculated in the perspective of searching for a possible signature of the source in the experimental spectra [3, 4]. A common feature of these studies is that the calculated fluxes are extremely small in intensity with their spectra peaked at low momenta. This requires the secondary galactic contribution to be accurately known for a significant search of the former to be considered. Another motivation for a careful examination of the antimatter production in the Galaxy is provided by the need of evaluating the galactic flux which will constitute a physical background for the forthcoming new experiments to search for primordial antimatter in the universe [5, 6, 7, 8]. The evaluation can be performed using the

New constraints on the cosmic mid-infrared background using TeV gamma-ray astronomy

Very high energy gamma-ray data obtained by CAT and HEGRA from active galactic nucleus Mkn 501 are used to constrain the cosmic Mid-Infrared background. While the entire infrared and submillimeter spectrum shape based on models has been fixed and the density scaled as a whole in previous studies, recent measures on the low and high energy infrared background are extensively used in this paper. In this original approach, the infrared distribution is only varied in the unexplored 3.5-100 microns region. With conservative hypothesis on the intrinsic spectra of Mkn 501, an upper limit of 4.7 nW.m-2.sr-1 between 5 and 15 microns is derived, which is very close to the lower limit inferred from deep ISOCAM cosmological surveys at 15 microns. This result is shown to be independent of the exact density of the lambda 100 microns infrared distribution within the uncertainties of the measurements. Moreover, the study presented here rules out a complete extragalactic origin for the 60 microns excess found by Finkbeiner et al. (2000).

Antiprotons from primordial black holes

Primordial black holes (pbhs) have motivated many studies since it was shown that they should evap- orate and produce all kinds of particles (Hawking 1974). Recent experimental measurements of cosmic rays with great accuracy, theoretical investigations on the possible formation mechanisms and detailed evaporation pro- cesses have revived the interest in such astrophysical objects. This article aims to use the latest developments in antiproton propagation models (Maurin et al. 2001; Donato et al. 2001) together with new data from BESS, CAPRICE and AMS experiments to constrain the local amount of pbh dark matter. Depending on the diusion halo parameters and on the details of the emission mechanisms, we derive an average upper limit of the order of PBH 1:7 10 33 gc m 3 .

Kaluza-Klein dark matter and Galactic antiprotons

Extra dimensions offer new ways to address long-standing problems in beyond-the-standard-model particle physics. In some classes of extra-dimensional models, the lightest Kaluza-Klein particle is a viable dark matter candidate. In this work, we study indirect detection of Kaluza-Klein dark matter via its annihilation into antiprotons. We use a sophisticated galactic cosmic ray diffusion model whose parameters are fully constrained by an extensive set of experimental data. We find that models with universal extra dimensions remain unconstrained by cosmic ray antiprotons while low-mass weakly interacting massive particle candidates of a few tens of GeV that arise in Randall-Sundrum geometries can be probed.

Gauss-Bonnet black holes at the LHC: Beyond the dimensionality of space

Abstract The Gauss–Bonnet invariant is one of the most promising candidates for a quadratic curvature correction to the Einstein action in expansions of supersymmetric string theory. We study the evaporation of such Schwarzschild–Gauss–Bonnet black holes which could be formed at future colliders if the Planck scale is of order of TeV, as predicted by some modern brane world models. We show that, beyond the dimensionality of space, the corresponding coupling constant could be measured by the LHC. This opens new windows for physics investigation in spite of the possible screening of microphysics due to the event horizon.

Gravitino production by primordial black hole evaporation and constraints on the inhomogeneity of the early universe

In supergravity models, the evaporation of light primordial black holes should be a source of gravitinos. By considering this process, new stringent limits are derived on the abundance of small black holes with initial masses less than 109 g. In minimal supergravity, the subsequent decay of evaporated gravitinos into cascades of non-equilibrium particles leads to the formation of elements whose abundance is constrained by observations. In gauge mediated supersymmetry breaking models, their density is required not to overclose the universe. As a result, cosmological models with substantial inhomogeneities on small scales are excluded.

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 nontrivial coupling between black holes and quantum fields during the evaporation process: they can be used both from a theoretical viewpoint to investigate the intricate space-time 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 favor of the bulk channel in particular frequency regimes.

Origin of the high energy proton component below the geomagnetic cutoff in near earth orbit

Abstract The high flux proton component observed by AMS below the geomagnetic cutoff can be well accounted for by assuming these particles to be secondaries originating from the interaction of cosmic ray protons with the atmosphere. Simulation results are reported.