Massive Photon and Dark Energy
  We investigate cosmology of massive electrodynamics and explore the
possibility whether massive photon could provide an explanation of the dark
energy. The action is given by the scalar-vector-tensor theory of gravity which
is obtained by non-minimal coupling of the massive Stueckelberg QED with
gravity and its cosmological consequences are studied by paying a particular
attention to the role of photon mass. We find that the theory allows
cosmological evolution where the radiation- and matter-dominated epochs are
followed by a long period of virtually constant dark energy that closely mimics
$\Lambda$CDM model and the main source of the current acceleration is provided
by the nonvanishing photon mass governed by the relation $\Lambda\sim m^2$. A
detailed numerical analysis shows that the nonvanishing photon mass of the
order of $\sim 10^{-34}$ eV is consistent with the current observations. This
magnitude is far less than the most stringent limit on the photon mass
available so far, which is of the order of $m \leq 10^{-27}$eV.
