Measuring the 13-mixing angle and the CP phase with neutrino telescopes

The observed excess of high-energy cosmic rays from the Galactic plane in the energy range \sim 10^18 eV may be naturally explained by neutron primaries generated in the photo-dissociation of heavy nuclei. In this scenario, neutrons with lower energy decay before reaching the Earth and produce a detectable flux in a 1 km^3 neutrino telescope. The initial flavor composition of these neutrinos, \phi(\bar\nu_e):\phi(\bar\nu_\mu):\phi(\bar\nu_\tau)=1:0:0, offers the opportunity to perform a combined \bar\nu_\mu/\bar\nu_\tau appearance and \bar\nu_e disappearance experiment. The observable ratio \phi(\bar\nu_\mu)/\phi(\bar\nu_e+\bar\nu_\tau) of fluxes arriving on Earth depends appreciably on the 13-mixing angle \theta_13 and the leptonic CP phase \delta_CP, opening thus a new experimental avenue to measure these two quantities.Comment: 4 pages, 2 eps figures. Enlarged discussion, references added. Matches version to appear in PR

The GZK horizon and constraints on the cosmic ray source spectrum from observations in the GZK regime

We discuss the GZK horizon of protons and present a method to constrain the injection spectrum of ultrahigh energy cosmic rays (UHECRs) from supposedly identified extragalactic sources. This method can be applied even when only one or two events per source are observed and is based on the analysis of the probability for a given source to populate different energy bins, depending on the actual CR injection spectral index. In particular, we show that for a typical source density of $4\times 10^{-5} Mpc^{-3}$, a data set of 100 events above $6\times 10^{19}$ eV allows one in 97% of all cases to distinguish a source spectrum $dN/dE\propto E^{-1.1}$ from one with $E^{-2.7}$ at 95% confidence level.Comment: v2: 5 pages, 3 figures; shortened, title changed, matches version to be publishe

The Compton-Getting effect on ultra-high energy cosmic rays of cosmological origin

Deviations from isotropy have been a key tool to identify the origin and the primary type of cosmic rays at low energies. We suggest that the Compton-Getting effect can play a similar role at ultra-high energies: If at these energies the cosmic ray flux is dominated by sources at cosmological distances, then the movement of the Sun relative to the cosmic microwave background frame induces a dipole anisotropy at the 0.6% level. The energy dependence and the orientation of this anisotropy provide important information about the transition between galactic and extragalactic cosmic rays, the charge of the cosmic ray primaries, the galactic magnetic field and, at the highest energies, the energy-loss horizon of cosmic rays. A 3-sigma detection of this effect requires around 10^6 events in the considered energy range and is thus challenging but not impossible with present detectors. As a corollary we note that the Compton-Getting effect allows one also to constrain the fraction of the diffuse gamma-ray background emitted by sources at cosmological distance, with promising detection possibilities for the GLAST satellite.Comment: v2: 5 pages, no figure. Minor changes, matches published versio

Filamentary Diffusion of Cosmic Rays on Small Scales

We investigate the diffusion of cosmic rays (CR) close to their sources. Propagating individual CRs in purely isotropic turbulent magnetic fields with maximal scale of spatial variations Lmax, we find that CRs diffuse anisotropically at distances r <~ Lmax from their sources. As a result, the CR densities around the sources are strongly irregular and show filamentary structures. We determine the transition time t* to standard diffusion as t* ~ 10^4 yr (Lmax/150 pc)^b (E/PeV)^(-g) (Brms/4 muG)^g, with b ~ 2 and g = 0.25-0.5 for a turbulent field with Kolmogorov power spectrum. We calculate the photon emission due to CR interactions with gas and the resulting irregular source images.Comment: 5 pages (2 columns), 4 figures. Published in Physical Review Letter

Limiting SUSY-QCD spectrum and its application for decays of superheavy particles

The supersymmetric generalization of the limiting and Gaussian QCD spectra is obtained. These spectra are valid for $x \ll 1$, when the main contribution to the parton cascade is given by gluons and gluinos. The derived spectra are applied to decaying superheavy particles with masses up to the GUT scale. These particles can be relics from the Big Bang or produced by topological defects and could give rise to the observed ultrahigh energy cosmic rays. General formulae for the fluxes of protons, photons and neutrinos due to decays of superheavy particles are obtained.Comment: 8 pages, revtex, 3 ps figures. v2 minor changes, v3 typo in eq.(15) corrected; version to appear in Phys. Lett.

Antimatter production in supernova remnants

We calculate the energy spectra of cosmic rays (CR) and their secondaries produced in a supernova remnant (SNR), taking into account the time-dependence of the SNR shock. We model the trajectories of charged particles as a random walk with a prescribed diffusion coefficient, accelerating the particles at each shock crossing. Secondary production by CRs colliding with gas is included as a Monte Carlo process. We find that SNRs produce less antimatter than suggested previously: The positron/electron ratio and the antiproton/proton ratio are a few percent and few $\times 10^{-5}$, respectively. Moreover, the obtained positron/electron ratio decreases with energy, while the antiproton/proton ratio rises at most by a factor of two above 10 GeV.Comment: 8 pages, 8 eps figures; extended version of arXiv:1004.1118; v2: minor corrections, matches published versio

Restricting UHECRs and cosmogenic neutrinos with Fermi-LAT

Ultrahigh energy cosmic ray (UHECR) protons interacting with the cosmic microwave background (CMB) produce UHE electrons and gamma-rays that in turn initiate electromagnetic cascades on CMB and infrared photons. As a result, a background of diffuse isotropic gamma radiation is accumulated in the energy range E\lsim 100 GeV. The Fermi-LAT collaboration has recently reported a measurement of the extragalactic diffuse background finding it less intense and softer than previously measured by EGRET. We show that this new result constrains UHECR models and the flux of cosmogenic neutrinos. In particular, it excludes models with cosmogenic neutrino fluxes detectable by existing neutrino experiments, while next-generation detectors as e.g. JEM-EUSO can observe neutrinos only for extreme parameters.Comment: 7 pages, 6 eps figures; v2: minor changes, v3: final version, added discussion of EGMF influenc

Search for photons at the Pierre Auger Observatory

The Pierre Auger Observatory has a unique potential to search for ultra-high energy photons (above ~1 EeV). First experimental limits on photons were obtained during construction of the southern part of the Observatory. Remarkably, already these limits have proven useful to falsify proposals about the origin of cosmic rays, and to perform fundamental physics by constraining Lorentz violation. A final discovery of photons at the upper end of the electromagnetic spectrum is likely to impact various branches of physics and astronomy.Comment: 5 pages, 5 figures. Presented at CRIS 2008, Malfa, Ital

Curvature Radiation by Ultrarelativistic Protons

We study pion curvature radiation by a proton, i.e. pion emission by a proton moving along a curved trajectory. We suggest an approximate semiclassical solution and the exact solution for which we assume that a proton moves in a fictitious magnetic field with the Larmor radius equal to the curvature radius of the real trajectory. As possible application we consider the pion radiation by ultrahigh energy protons moving along curved magnetic field lines. Such situation can occur in the magnetosphere of a young pulsar, in the magnetosphere of the accretion disk around a black hole, and in the vicinity of a superconducting cosmic string. The decay products of these pions, such as high energy photons or neutrinos, can give the observable consequences of the considered mechanism.Comment: 5 pages, revtex, to appear in Physics Letters

Reconciling the ultra-high energy cosmic ray spectrum with Fermi shock acceleration

The energy spectrum of ultra-high energy cosmic rays (UHECR) is usually calculated for sources with identical properties. Assuming that all sources can accelerate UHECR protons to the same extremely high maximal energy E_max > 10^{20} eV and have the steeply falling injection spectrum 1/E^{2.7}, one can reproduce the measured cosmic ray flux above E > 10^{18} eV. We show that relaxing the assumption of identical sources and using a power-law distribution of their maximal energy allows one to explain the observed UHECR spectrum with the injection 1/E^2 predicted by Fermi shock acceleration.Comment: v2: extended discussio