Dark Matter Axions Revisited
  We study for what specific values of the theoretical parameters the axion can
form the totality of cold dark matter. We examine the allowed axion parameter
region in the light of recent data collected by the WMAP5 mission plus baryon
acoustic oscillations and supernovae, and assume an inflationary scenario and
standard cosmology. If the Peccei-Quinn symmetry is restored after inflation,
we recover the usual relation between axion mass and density, so that an axion
mass $m_a =67\pm2{\rm \mu eV}$ makes the axion 100% of the cold dark matter. If
the Peccei-Quinn symmetry is broken during inflation, the axion can instead be
100% of the cold dark matter for $m_a < 15{\rm meV}$ provided a specific value
of the initial misalignment angle $\theta_i$ is chosen in correspondence to a
given value of its mass $m_a$. Large values of the Peccei-Quinn symmetry
breaking scale correspond to small, perhaps uncomfortably small, values of the
initial misalignment angle $\theta_i$.
