Void magnetic field and its primordial origin in inflation
  Since magnetic fields in galaxies, galactic clusters and even void regions
are observed, theoretical attempts to explain their origin are strongly
motivated. It is interesting to consider that inflation is responsible for the
origin of the magnetic fields as well as the density perturbation. However, it
is known that inflationary magnetogenesis suffers from several problems. We
explore these problems by using a specific model, namely the kinetic coupling
model, and show how the model is constrained. Model independent arguments are
also discussed.
