On the viability of a certain vector-tensor theory of gravitation
  A certain vector-tensor theory is revisited. Our attention is focused on
cosmology. Against previous suggestions based on preliminary studies, it is
shown that, if the energy density of the vector field is large enough to play
the role of the dark energy and its fluctuations are negligible, the theory is
not simultaneously compatible with current observations on: supernovae, the
cosmic microwave background (CMB) anisotropy, and the power spectrum of the
energy density fluctuations. However, for small enough energy densities of the
vector field, the theory becomes compatible with all the above observations
and, moreover, it leads to an interesting evolution of the so-called vector
cosmological modes. This evolution appears to be different from that of general
relativity, and the difference might be useful to explain the anomalies in the
low order CMB multipoles.
