Late-time magnetogenesis driven by ALP dark matter and dark photon

Kiwoon Choi; Hyungjin Kim; Toyokazu Sekiguchi

doi:10.1103/PhysRevLett.121.031102

paper

Late-time magnetogenesis driven by ALP dark matter and dark photon

arXiv:1802.07269 · doi:10.1103/PhysRevLett.121.031102

Abstract

We propose a mechanism generating primordial magnetic fields after the $e^{+} e^{-}$ annihilations. Our mechanism involves an ultra-light axion-like 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 $1 0^{- 21} eV ≲ m_{ϕ} ≲ 1 0^{- 17} eV$ , our mechanism can generate $B \sim 1 0^{- 24} G (m_{ϕ} /1 0^{- 17} eV)^{5/4}$ with a coherent length $λ \sim (m_{ϕ} /1 0^{- 17} eV)^{- 1/2}$ 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 $E_{X} \sim B_{X} \sim 80 nG (m_{ϕ} /1 0^{- 17} eV)^{- 1/4}$ , which can result in interesting astrophysical/cosmological phenomena by inducing the mixings between the ALP, ordinary photon, and dark photon states.

6 pages, 2 figures; discussions rearranged, minor numerical errors fixed, conclusion unchanged; discussion improved, accepted for publication in PRL

Late-time magnetogenesis driven by ALP dark matter and dark photon

Abstract

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