Magnetic fields in the Universe potentially serve as messengers of primordial physics. The observationally suggested intergalactic magnetic fields may be a relic of helical primordial $\mathrm{U}(1{)}_Y$ magnetic fields, which may also explain the origin of the baryon asymmetry of the Universe. This scenario has been considered not to be viable, which we revisit as well as the baryon isocurvature problem for nonhelical primordial $\mathrm{U}(1{)}_Y$ magnetic fields, based on the recent discussion on the hot electroweak theory. We find that maximally helical fields can be the origin of both the intergalactic magnetic fields and the baryon asymmetry of the Universe and that there can be a window for nonhelical fields to explain the origin of the intergalactic magnetic fields if the Higgs dynamics during the electroweak crossover compensate the helicity decay with a $\lesssim {10}^{-9--10}$ precision.

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• Baryogenesis & leptogenesis
• Electroweak symmetry breaking
• Primordial magnetic fields