On the Measurement of the Helicity of Intergalactic Magnetic Fields Using Ultra-High-Energy Cosmic Rays

TL;DR

This paper proposes a method to measure the helicity of intergalactic magnetic fields by analyzing the arrival directions of ultra-high-energy cosmic rays, offering a new probe into the early universe's magnetogenesis.

Contribution

It demonstrates the feasibility of using UHECRs' arrival distributions to determine the helicity and its sign of intergalactic magnetic fields through simulation-based analysis.

Findings

First harmonic moments can reveal the absolute value of magnetic helicity.

The sign of the helicity can be inferred from the distribution asymmetry.

Simulations show potential for constraining primordial magnetic field properties.

Abstract

The origin of the first magnetic fields in the Universe is a standing problem in cosmology. Intergalactic magnetic fields (IGMFs) may be an untapped window to the primeval Universe, providing further constrains on magnetogenesis. We demonstrate the feasibility of using ultra-high-energy cosmic rays (UHECRs) to constrain the helicity of IGMFs by performing simulations of cosmic-ray propagation in simple magnetic field configurations. We show that the first harmonic moments of the arrival distribution of UHECRs may be used to measure the absolute value of the helicity and its sign.