Magnetic Helicity Generation from the Cosmic Axion Field
Abstract
Description
The coupling between a primordial magnetic field and the cosmic axion field generates a helical component of the magnetic field around the time in which the axion starts to oscillate. If the energy density of the seed magnetic field is comparable to the energy density of the universe at that time, then the resulting magnetic helicity is about |H_B| \simeq (10^{-20} G)^2 kpc and remains constant after its generation. As a corollary, we find that the standard properties of the oscillating axion remain unchanged even in the presence of very strong magnetic fields.
6 pages, 2 figures. Accepted for publication in Phys. Rev. D. Minor revisions and new references added
6 pages, 2 figures. Accepted for publication in Phys. Rev. D. Minor revisions and new references added