Baryon isocurvature constraints on the primordial hypermagnetic fields

TL;DR

This paper investigates whether primordial hypermagnetic fields can simultaneously explain baryogenesis and intergalactic magnetic fields, concluding that current baryon isocurvature constraints rule out such scenarios before electroweak symmetry breaking.

Contribution

It demonstrates that primordial magnetogenesis before electroweak symmetry breaking cannot account for both phenomena due to baryon isocurvature constraints.

Findings

Primordial hypermagnetic fields cannot produce observed baryon asymmetry without conflicting with nucleosynthesis constraints.

Fully helical magnetic fields are insufficient to explain intergalactic magnetic fields.

Constraints on baryon isocurvature perturbations rule out early magnetogenesis scenarios.

Abstract

It has been pointed out that hypermagnetic helicity decay at the electroweak symmetry breaking may have produced the observed baryon asymmetry of the Universe through the chiral anomaly in the standard model of particle physics. Although fully helical magnetic field that can adequately produce the observed baryon asymmetry is not strong enough to explain the origin of the intergalactic magnetic field inferred by the Fermi satellite, the mixture of helical and nonhelical primordial magnetic fields may explain both baryogenesis and the intergalactic magnetic fields simultaneously. We first show that such a scenario is ruled out by the constraint on the amplitude of baryon isocurvature perturbations produced by the primordial magnetic fields to avoid overproduction of deuterium at the big bang nucleosynthesis. Then we show that any attempt to explain the origin of intergalactic magnetic field by primordial magnetogenesis before the electroweak symmetry breaking does not work due to the above constraint irrespective of the helicity and baryogenesis mechanism.