http://arxiv.org/abs/1310.4826
Motivated by the possible existence of a cosmological magnetic field with non-trivial helicity, we evaluate a CP odd statistic, $Q$, using gamma ray data obtained from Fermi satellite observations at high galactic latitudes. Observed values of $Q$ are found to be non-zero at the $2\sigma$ level ($3\sigma$ in the northern hemisphere) and also deviate at the same level from values obtained from simulated data. Contamination from the Milky Way does not seem to be responsible for the excess since the signal is present even for data at very high galactic latitudes. Assuming that the excess is indeed due to a helical cosmological magnetic field, our results indicate left-handed magnetic helicity and field strength $\sim 10^{-14} {\rm G}$ on $\sim 10 {\rm Mpc}$ scales.
Date added: Mon, 21 Oct 13