Abstract
Primordial magnetic fields in the dark sector can be transferred to magnetic fields in the visible sector due to a gauge kinetic mixing term. We show that the transfer occurs when the evolution of magnetic fields is dominated by dissipation due to finite electric conductivity, and does not occur at later times if the magnetic fields evolve according to magnetohydrodynamics scaling laws. The efficiency of the transfer is suppressed by not only the gauge kinetic mixing coupling but also the ratio between the large electric conductivity and the typical momentum of the magnetic fields. We find that the transfer gives nonzero visible magnetic fields today. However, without possible dynamo amplifications, the field transfer is not efficient enough to obtain the intergalactic magnetic fields suggested by the gamma-ray observations, although there are plenty of possibilities for efficient dark magnetogenesis, which are experimentally unconstrained.
Highlights
Primordial magnetic fields have been of interest for many years since they may explain the observed galaxy and galaxy cluster magnetic fields through the dynamo mechanism during structure formation [1]
We have examined how dark magnetic fields can be transferred to the visible magnetic fields through the gauge kinetic mixing
We have considered the system with the Lagrangian Eq (1) where there are independent dark and visible U(1) currents in the basis with gauge kinetic mixing
Summary
Primordial magnetic fields have been of interest for many years since they may explain the observed galaxy and galaxy cluster magnetic fields through the dynamo mechanism during structure formation [1]. There have been many proposals for primordial magnetogenesis, such as the inflationary magnetogenesis [19,20,21,22], productions from the first-order phase transition of the electroweak symmetry [23,24,25] or QCD [26,27,28], or productions through the chiral instability [29,30,31] It remains to be seen if these proposals can match magnetic field spectra as indicated by the blazar observations Unless further amplification of the magnetic field occurs, e.g., at the time of dark U(1) symmetry breaking, the suppression factor implies that the visible fields are too weak to explain the blazar observations.
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