Low-Scale Inflationary Magnetogenesis without Baryon Isocurvature Problem

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.