title: Cosmological magnetic field: a fossil of density perturbations in the early universe.
abstract: The origin of the substantial magnetic fields that are found in galaxies and on even larger scales, such as in clusters of galaxies, is yet unclear. If the second-order couplings between photons and electrons are considered, then cosmological density fluctuations, which explain the large-scale structure of the universe, can also produce magnetic fields on cosmological scales before the epoch of recombination. By evaluating the power spectrum of these cosmological magnetic fields on a range of scales, we show here that magnetic fields of 10(-18.1) gauss are generated at a 1-megaparsec scale and can be even stronger at smaller scales (10(-14.1) gauss at 10 kiloparsecs). These fields are large enough to seed magnetic fields in galaxies and may therefore have affected primordial star formation in the early universe.
authors.affiliation: National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan. ichiki@th.nao.ac.jp
authors.forename: Kiyotomo
authors.initials: K
authors.lastname: Ichiki
authors.forename: Keitaro
authors.initials: K
authors.lastname: Takahashi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ohno
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Hanayama
authors.forename: Naoshi
authors.initials: N
authors.lastname: Sugiyama