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Title: Do intergalactic magnetic fields carry net helicity?
Plain: Magnetic fields produced in the early universe by processes that distinguish left from right would be twisted with a preferred handedness. Measuring that twist would point to their origin.
Precise: Measure the magnetic helicity of void fields through parity-odd correlations in the arrival directions and energies of cascade $\gamma$ rays (the $Q$ statistic of Tashiro and Vachaspati) or through Faraday rotation. CP-violating magnetogenesis (for example during baryogenesis) predicts maximal helicity of one sign. An answer is a detection with sign, or a bound on the helical fraction.
Settled by: Parity-odd statistics of diffuse GeV gamma rays from Fermi and future gamma-ray telescopes with controlled Galactic foregrounds.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)