Late-Time Magnetogenesis Driven by Axionlike Particle Dark Matter and a Dark Photon

Abstract

We propose a mechanism generating primordial magnetic fields after the e(+)e(-) annihilations. Our mechanism involves an ultralight axionlike particle (ALP) which constitutes the dark matter and a dark U(1)(X) gauge boson introduced to bypass the obstacle placed by the conductivity of cosmic plasma. In our scheme, a coherently oscillating ALP amplifies the dark photon field, and part of the amplified dark photon field is concurrently converted to the ordinary magnetic field through the ALP-induced magnetic mixing. For the relevant ALP mass range 10(-21) eV less than or similar to m(phi) <= 10(-17) eV, our mechanism can generate B similar to 10(-24) G(m(phi)/10(-17) eV)(5/4) with a coherent length lambda similar to (m(phi)/10(-17) eV)(-1/2) kpc, which is large enough to provide a seed of the galactic magnetic fields. The mechanism also predicts a dark U(1)(X) electromagnetic field E-X similar to B-X similar to 80 nG(m(phi)/10(-17) eV)(-1/4), which can result in interesting astrophysical or cosmological phenomena by inducing the mixings between the ALP, ordinary photon, and dark photon states ⓒ2018 American Physical Society