  Primordial magnetogenesis is an intriguing possibility to explain the origin
of intergalactic magnetic fields (IGMFs). However, the baryon isocurvature
problem has recently been pointed out, ruling out all magnetogenesis models
operating above the electroweak scale. In this letter, we show that lower-scale
inflationary scenarios with a Chern-Simons coupling can evade this problem. We
propose concrete inflationary models whose reheating temperatures are lower
than the electroweak scale and numerically compute the amount of magnetic
fields generated during inflation and reheating. We find that, for lower
reheating temperatures, the magnetic helicity decreases significantly. It is
also possible to generate fully helical magnetic fields by modifying the
inflaton potential. In both cases, the produced magnetic fields can be strong
enough to explain the observed IGMFs, while avoiding the baryon isocurvature
problem.
