Filtering and aliasing effects produced by time-discretization in the simulation of Extensive Air Shower radio signals

Extensive Air Showers (EAS) triggered by high-energy particles can generate short radio pulses, allowing the indirect study of ultra high energy (UHE) cosmic rays or neutrinos with sparse arrays of antennas. Accurate simulation of EAS and the radio pulses they generate is key in informing the design and detection capability of such arrays. These simulations are usually carried out with either the CoREAS or the ZHAireS simulation packages, which are considered to be the state-of-the-art in the field. In this work, it is pointed out for the first time that the time-discretization processes used in these packages lead to filtering and aliasing effects even though, at first glance, the Nyquist-Shannon sampling criterion seems to be respected. These effects are significant if the receiving antenna is located close to the EAS Cherenkov angle. We give an overview of the causes behind this effect, and suggestions on how to solve it or circumvent it.