Low-Scale Inflationary Magnetogenesis without Baryon Isocurvature Problem

TL;DR

This paper proposes low-scale inflation models with Chern-Simons coupling that generate primordial magnetic fields strong enough to explain intergalactic magnetic fields, while avoiding the baryon isocurvature problem associated with high-scale models.

Contribution

It introduces concrete low-scale inflationary models with reheating temperatures below the electroweak scale that successfully produce magnetic fields without baryon isocurvature issues.

Findings

Magnetic helicity decreases with lower reheating temperatures.

Fully helical magnetic fields can be generated by modifying the inflaton potential.

Generated magnetic fields can explain observed intergalactic magnetic fields.

Abstract

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.