Effects of the galactic magnetic field upon large scale anisotropies of extragalactic Cosmic Rays

The large scale pattern in the arrival directions of extragalactic cosmic rays that reach the Earth is different from that of the flux arriving to the halo of the Galaxy as a result of the propagation through the galactic magnetic field. Two different effects are relevant in this process: deflections of trajectories and (de)acceleration by the electric field component due to the galactic rotation. The deflection of the cosmic ray trajectories makes the flux intensity arriving to the halo from some direction to appear reaching the Earth from another direction. This applies to any intrinsic anisotropy in the extragalactic distribution or, even in the absence of intrinsic anisotropies, to the dipolar Compton-Getting anisotropy induced when the observer is moving with respect to the cosmic rays rest frame. For an observer moving with the solar system, cosmic rays traveling through far away regions of the Galaxy also experience an electric force coming from the relative motion (due to the rotation of the Galaxy) of the local system in which the field can be considered as being purely magnetic. This produces small changes in the particles momentum that can originate large scale anisotropies even for an isotropic extragalactic flux.Comment: 11 pages, 4 figure

Recent results from the Pierre Auger Observatory

The main results from the Auger Observatory are described. A steepening of the spectrum is observed at the highest energies, supporting the expectation that above $4\times 10^{19}$ eV the cosmic ray energies are significantly degraded by interactions with the CMB photons (the GZK effect). This is further supported by the correlations observed above $6\times 10^{19}$ eV with the distribution of nearby active galaxies, which also show the potential of Auger to start the era of charged particle astronomy. The lack of observation of photons or neutrinos strongly disfavors top-down models, and these searches may approach in the long term the sensitivity required to test the fluxes expected from the secondaries of the very same GZK process. Bounds on the anisotropies at EeV energies contradict hints from previous experiments that suggested a large excess from regions near the Galactic centre or the presence of a dipolar type modulation of the cosmic ray flux.Comment: 6 p., 8 figs., proceedings of the XXIII International Conference on Neutrino Physics and Astrophysics (Neutrino 08

Directed abelian algebras and their applications to stochastic models

To each directed acyclic graph (this includes some D-dimensional lattices) one can associate some abelian algebras that we call directed abelian algebras (DAA). On each site of the graph one attaches a generator of the algebra. These algebras depend on several parameters and are semisimple. Using any DAA one can define a family of Hamiltonians which give the continuous time evolution of a stochastic process. The calculation of the spectra and ground state wavefunctions (stationary states probability distributions) is an easy algebraic exercise. If one considers D-dimensional lattices and choose Hamiltonians linear in the generators, in the finite-size scaling the Hamiltonian spectrum is gapless with a critical dynamic exponent $z = D$. One possible application of the DAA is to sandpile models. In the paper we present this application considering one and two dimensional lattices. In the one dimensional case, when the DAA conserves the number of particles, the avalanches belong to the random walker universality class (critical exponent $\sigma_{\tau} = 3/2$). We study the local densityof particles inside large avalanches showing a depletion of particles at the source of the avalanche and an enrichment at its end. In two dimensions we did extensive Monte-Carlo simulations and found $\sigma_{\tau} = 1.782 \pm 0.005$.Comment: 14 pages, 9 figure