Large-scale magnetic fields can explain the baryon asymmetry of the Universe

TL;DR

This paper proposes that large-scale helical magnetic fields in the early Universe can generate the observed baryon asymmetry through the chiral anomaly, aligning with blazar observations and providing new constraints on magnetic field strength.

Contribution

It demonstrates that primordial helical hypermagnetic fields can produce baryon asymmetry without beyond-standard-model physics, using numerical solutions of the Boltzmann equation and deriving new bounds.

Findings

Baryon asymmetry can be explained by primordial magnetic fields with negative helicity.

The model aligns with observed large-scale magnetic fields from blazar data.

A tighter upper bound on magnetic field strength is established to prevent overproduction.

Abstract

Helical hypermagnetic fields in the primordial Universe can produce the observed amount of baryon asymmetry through the chiral anomaly without any ingredients beyond the standard model of particle physics. While they generate no $B-L$ asymmetry, the generated baryon asymmetry survives the spharelon washout effect, because the generating process remains active until the electroweak phase transition. Solving the Boltzmann equation numerically and finding an attractor solution, we show that the baryon asymmetry of our Universe can be explained, if the present large-scale magnetic fields indicated by the blazar observations have a negative helicity and existed in the early Universe before the electroweak phase transition. We also derive the upper bound on the strength of the helical magnetic field, which is tighter than the cosmic microwave background constraint, to avoid the overproduction of baryon asymmetry.