Full sky harmonic analysis hints at large UHECR deflections
  The full-sky multipole coefficients of the ultra-high energy cosmic ray
(UHECR) flux have been measured for the first time by the Pierre Auger and
Telescope Array collaborations using a joint data set with E > 10 EeV. We
calculate these harmonic coefficients in the model where UHECR are protons and
sources trace the local matter distribution, and compare our results with
observations. We find that the expected power for low multipoles (dipole and
quadrupole, in particular) is sytematically higher than in the data: the
observed flux is too isotropic. We then investigate to which degree our
predictions are influenced by UHECR deflections in the regular Galactic
magnetic field (GMF). It turns out that the UHECR power spectrum coefficients
$C_\ell$ are quite insensitive to the effects of the GMF, so it is unlikely
that the discordance can be reconciled by tuning the GMF model. On the
contrary, a sizeable fraction of uniformly distributed flux (representing for
instance an admixture of heavy nuclei with considerably larger deflections) can
bring simulations and observations to an accord.
