International School of Cosmic Ray Astrophysics <<Maurice M. Shapiro>>

21^st Course: Astroparticle Physics: Yesterday, Today, and Tomorrow
1-7 August, 2018

After a short introduction I start with the key observations of galactic cosmic rays: (1) the high isotropy of their arrival directions, (2) 100 times more hadrons than electrons at relativistic energies, (3) nearly constant ux over the last 109 years. These observa- tions point to electromagnetic acceleration processes which order particle distribution functions with respect to their rigidity R = p=jZj. To a large extent, our progress in understanding cosmic ray dynamics in cosmic plasmas depends on our understanding of the magnetic and electric eld uctuations. Because of the observed energy equipartition between electromagnetic elds and cos- mic ray particles, a fully complete description of their dynamics is necessary accounting for their various nonlinear coupling and interaction processes: to determine the particle's phase space density from the collisionless Boltzmann equation we have to know the elec- tromagnetic eld; but to determine the electromagnetic eld from Maxwell's equations we have to know the phase space density of the particles determining the charge and current densities. We are facing the fundamental problem of plasma physics: the plasma particles determine the electromagnetic elds and vice versa in a highly nonlinear way. In order to proceed with a solution of this coupled problem two opposite points of view can be taken: 1) the test uctuation approach, discussed in Lectures 1 and 2, in which the plasma particle distribution functions are assumed to be given, so that the resulting electromag- netic eld and its properties can be calculated. 2) the test particle approach, discussed in Lectures 2 and 3, in which the electromag- netic eld is assumed to be given, so that the response of the particles can be calculated. A consistent theory should combine these two approaches at least to a level of avoiding dramatic contradictions.