Discrepancies in the Monte Carlo simulations of propagation of ultra-high energy cosmic-ray photons in the geomagnetic field

摘要

The discrepancies in the results produced by the two most commonly used MonteCarlo programs for simulation of propagation of ultra-high energy cosmic rayphotons in the presence of the geomagnetic field are presented. Althoughphotons have not yet been discovered in the cosmic ray flux at highestenergies, the capabilities of the present cosmic ray detectors make theirdiscovery possible, according to the predictions of conventional models, withinthe next few years. It is therefore necessary to have a reliable and wellmaintained software for relevant simulations. The results of this paper areimportant for simulations of propagation of photons at energies above 10^19 eV.Photons of such high energies might interact with the geomagnetic field givingrise to a cascade of particles even above the atmosphere. This effect is calleda "preshower effect". The preshower effect is important for air showerevolution and has to be accounted for in full Monte Carlo simulations ofpropagation of highest energy cosmic-ray photons. In this paper we compare thetwo most frequently used Monte Carlo codes for preshower simulations:PRESHOWER, used as a stand-alone program or as a part of CORSIKA, and MaGICS,used as a part of AIRES.