Origin of Cosmic Magnetic Fields

TL;DR

This paper demonstrates that quantum magnetic fluctuations during de Sitter inflation remain constant, leading to a scale-independent primordial magnetic field that can explain observed galactic magnetic fields.

Contribution

It provides a quantum field theoretical calculation showing magnetic fluctuations are preserved during inflation, challenging previous assumptions of their decay.

Findings

Quantum magnetic fluctuations remain constant during inflation.

The resulting magnetic field is scale independent with an intensity of ~10^{-12} G.

This primordial field can account for galactic magnetic fields.

Abstract

We calculate, in the free Maxwell theory, the renormalized quantum vacuum expectation value of the two-point magnetic correlation function in de Sitter inflation. We find that quantum magnetic fluctuations remain constant during inflation instead of being washed out adiabatically, as usually assumed in the literature. The quantum-to-classical transition of super-Hubble magnetic modes during inflation, allow us to treat the magnetic field classically after reheating, when it is coupled to the primeval plasma. The actual magnetic field is scale independent and has an intensity of few \times 10^(-12) G if the energy scale of inflation is few \times 10^(16) GeV. Such a field accounts for galactic and galaxy cluster magnetic fields.