We address some current theoretical issues around ultra-high energy cosmic rays. We recall that scenarios producing more γ−rays than cosmic rays up to high redshift can in general only provide a sub-dominant contribution to the ultra-high energy cosmic ray flux. This includes extra-galactic top-down and the Z-burst scenarios. Finally we discuss the influence of large scale cosmic magnetic field...

To understand the origin of ultra-high energy cosmic rays (UHECRs, defined to be above 10 eV), it is required to model in a realistic way their propagation in the Universe. UHECRs can interact with low energy radio, microwave, infrared and optical photons to produce electron/positron pairs or pions. The latter decay and give rise to neutrinos and electromagnetic cascades extending down to MeV e...

Propagation of cosmic rays (CRs) in turbulent and magnetized astrophysical media is a long-standing problem that requires both understanding the properties magnetic fields their interaction with energetic particles. This review focuses on selected recent theoretical findings made based progress simulating magnetohydrodynamic (MHD) turbulence. In particular, we address perpendicular parallel pro...

An understanding of how the heliosphere modulates galactic cosmic ray (GCR) fluxes and spectra is important, not only for studies of their origin, acceleration and propagation in our galaxy, but also for predicting their effects (on technology and on the Earth’s environment and organisms) and for interpreting abundances of cosmogenic isotopes in meteorites and terrestrial reservoirs. In contras...

The discrepancies in the results produced by the two most commonly used Monte Carlo programs for simulation of propagation of ultra-high energy cosmic ray photons in the presence of the geomagnetic field are presented. Although photons have not yet been discovered in the cosmic ray flux at highest energies, the capabilities of the present cosmic ray detectors make their discovery possible, acco...

Precision measurements of the electron component in the cosmic radiation provide important information about the origin and propagation of cosmic rays in the Galaxy. Here we present new results regarding negatively charged electrons between 1 and 625 GeV performed by the satellite-borne experiment PAMELA. This is the first time that cosmic-ray e⁻ have been identified above 50 GeV. The electron ...

In this work we reexamine the opacity of the cosmic background radiation to the propagation of extremely high energy cosmic rays. We use the continuous energy loss approximation to provide spectral modification factors for several hypothesized cosmic ray sources. Earlier problems with this approximation are resolved including the effects of resonances other than the ∆.

In recent years the variability of the cosmic ray flux has become one of the main issues interpreting cosmogenic elements and especially their connection with climate. In this review, an interdisciplinary team of scientists brings together our knowledge of the evolution and modulation of the cosmic ray flux from its origin in the Milky Way, during its propagation through the heliosphere, up to ...

The propagation of cosmic rays through the interstellar medium (ISM) inevitably produces LiBeB nuclei, and the accumulation of these elements over lifetime of galaxy can broadly account for the solar LiBeB abundances. Furthermore, data in old (Population II) stars provides crucial new information: the LiBeB trend versus heavy element abundances traces the Galactic evolution of LiBeB. We summari...