Speaker
Description
One of the most interesting open questions in high-energy astrophysics concerns the origin of ultra-high energy cosmic rays: during their propagation, these charged particles are deflected by extragalactic and Galactic magnetic fields and, as a result, their arrival directions do not point directly to their sources, making their correlation with possible sources non-trivial to determine.
Nonetheless, since ultra-high-energy cosmic ray particles cannot freely travel for cosmologically long distances, their distribution should follow the local distribution of matter in the universe to some extent: dipoles, quadrupoles and higher-order multipoles of their distribution in the sky are expected.
In 2017, significant evidence of a dipole anisotropy in the arrival direction of ultra-high energy cosmic rays with energies above 8 EeV towards a direction far away from the Galactic Center was found by the Collaboration, proving the extragalactic origin of those particles. However, no significant evidence of smaller-scale anisotropies has been found so far.
In our work, we explore the possibility of using harmonic correlators, such as the auto-correlation and the cross-correlation power spectra, to detect such anisotropies. In particular, the harmonic-space cross-correlation method, which consists of detecting the anisotropy in the ultra-high-energy cosmic ray flux through the harmonic-space power spectrum of the cross-correlation between ultra-high-energy cosmic ray counts and the distribution of galaxies, has not been yet employed in this context and could be more sensitive to smaller angular scales and more robust to systematic uncertainties than previously used methods, including the auto-correlation power spectrum.
