How isotropic can the UHECR flux be?

Understand

Modern observatories of ultra-high energy cosmic rays (UHECR) have collected over 10^4 events with energies above 10 EeV, whose arrival directions appear to be nearly isotropically distributed.

• On the other hand, the distribution of matter in the nearby Universe -- and, therefore, presumably also that of UHECR sources -- is not homogeneous.
• This is expected to leave an imprint on the angular distribution of UHECR arrival directions, though deflections by cosmic magnetic fields can confound the picture.
• In this work, we investigate quantitatively this apparent inconsistency.