Generation of magnetic fields in Einstein-Aether gravity
  Recently the lower bounds of the intergalactic magnetic fields $10^{-16} \sim
10^{-20}$ Gauss are set by gamma-ray observations while it is unlikely to
generate such large scale magnetic fields through astrophysical processes. It
is known that large scale magnetic fields could be generated if there exist
cosmological vector mode perturbations in the primordial plasma. The vector
mode, however, has only a decaying solution in General Relativity if the plasma
consists of perfect fluids. In order to investigate a possible mechanism of
magnetogenesis in the primordial plasma, here we consider cosmological
perturbations in the Einstein-Aether gravity model, in which the aether field
can act as a new source of vector metric perturbations and thus of magnetic
fields. We estimate the angular power spectra of temperature and B-mode
polarization of the Cosmic Microwave Background (CMB) Anisotropies in this
model and put a rough constraint on the aether field parameters from latest
observations. We then estimate the power spectrum of associated magnetic fields
around the recombination epoch within this limit. It is found that the spectrum
has a characteristic peak at $k=0.1 h{\rm Mpc^{-1}}$, and at that scale the
amplitude can be as large as $B\sim 10^{-22}$ Gauss where the upper bound comes
from CMB temperature anisotropies. The magnetic fields with this amplitude can
be seeds of large scale magnetic fields observed today if the sufficient dynamo
mechanism takes place. Analytic interpretation for the power spectra is also
given.
