Non-linear cosmic ray Galactic transport in the light of AMS-02 and Voyager data

Context: Features in the spectra of primary cosmic rays (CRs) provide invaluable information on the propagation of these particles in the Galaxy. In the rigidity region around a few hundred GV, such features have been measured in the proton and helium spectra by the PAMELA experiment and later confirmed with a higher significance by AMS-02. We investigate the implications of these datasets for the scenario in which CRs propagate under the action of self-generated waves. Aims: We show that the recent data on the spectrum of protons and helium nuclei as collected with AMS-02 and Voyager are in very good agreement with the predictions of a model in which the transport of Galactic CRs is regulated by self-generated waves. We also study the implications of the scenario for the boron-to-carbon ratio: although a good overall agreement is found, at high energy we find marginal support for a (quasi) energy independent contribution to the grammage, that we argue may come from the sources themselves Results: A break in the spectra of all nuclei is found at rigidity of a few hundred GV, as a result of a transition from self-generated waves to pre-existing waves with a Kolmogorov power spectrum. Neither the slope of the diffusion coefficient, nor its normalisation are free parameters. Moreover, at rigidities below a few GV, CRs are predicted to be advected with the self-generated waves at the local Alfv\'en speed. This effect, predicted in our previous work, provides an excellent fit to the Voyager data on the proton and helium spectra at low energies, providing additional support to the model.Comment: Submitted to A&A Research Note, 5 pages, 4 Figures. arXiv admin note: text overlap with arXiv:1306.201

Dark matter distribution in the universe and ultra-high energy cosmic rays

Two of the greatest mysteries of modern physics are the origin of the dark matter in the universe and the nature of the highest energy particles in the cosmic ray spectrum. We discuss here possible direct and indirect connections between these two problems, with particular attention to two cases: in the first we study the local clustering of possible sources of ultra-high energy cosmic rays (UHECRs) driven by the local dark matter overdensity. In the second case we study the possibility that UHECRs are directly generated by the decay of weakly unstable super heavy dark matter.Comment: 15 pages, 7 figures. Invited Talk at the "International Workshop on observing UHECRs from space and earth", August 9-12, 2000, Metepec, Puebla (Mexico

Opening the ultra high energy cosmic ray window from the top

While several arguments can be proposed against the existence of particles with energy in excess of $(3-5)\times 10^{19}$ eV in the cosmic ray spectrum, these particles are actually observed and their origin seeks for an explanation. After a description of the problems encountered in explaining these ultra-high energy cosmic rays (UHECRs) in the context of astrophysical sources, we will review the so-called {\it Top-Down} (TD) Models, in which UHECRs are the result of the decay of very massive unstable particles, possibly created in the Early Universe. Particular emphasis will be given to the signatures of the TD models, likely to be accessible to upcoming experiments like Auger.Comment: 13 pages, 3 figures. Invited Talk at the Vulcano Workshop `Frontier Objects in Astrophysics and Particle Physics', May 22-27, 200

Multi-Layer Hydrostatic Equilibrium of Planets and Synchronous Moons: Theory and Application to Ceres and to Solar System Moons

The hydrostatic equilibrium of multi-layer bodies lacks a satisfactory theoretical treatment despite its wide range of applicability. Here we show that by using the exact analytical potential of homogeneous ellipsoids we can obtain recursive analytical solutions and an exact numerical method for the hydrostatic equilibrium shape problem of multi-layer planets and synchronous moons. The recursive solutions rely on the series expansion of the potential in terms of the polar and equatorial shape eccentricities, while the numerical method uses the exact potential expression. These solutions can be used to infer the interior structure of planets and synchronous moons from the observed shape, rotation, and gravity. When applied to dwarf planet Ceres, we show that it is most likely a differentiated body with an icy crust of equatorial thickness 30-90 km and a rocky core of density 2.4-3.1 g/cm$^3$. For synchronous moons, we show that the $J_2/C_{22} \simeq 10/3$ and the $(b-c)/(a-c) \simeq 1/4$ ratios have significant corrections of order $\Omega^2/(\pi G \rho)$, with important implications on how their gravitational coefficients are determined from flyby radio science data and on how we assess their hydrostatic equilibrium state.Comment: 12 pages, 6 figures, in press in Ap