Do intergalactic magnetic fields carry net helicity?
In plain words
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 statement
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.
What would settle it
Parity-odd statistics of diffuse GeV gamma rays from Fermi and future gamma-ray telescopes with controlled Galactic foregrounds.
Parent problems
- Special case of Were cosmic magnetic seed fields primordial or astrophysical? · open · from revision 1 The parent was revised since revision 1: it now states another question.
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