On cosmic inflation in vector field theories
  We investigate the longitudinal ghost issue in Abelian vector inflation. It
turns out that, within the class of Lorentz-invariant vector field theories
with three degrees of freedom and without any extra (scalar) fields, the
possibilities are essentially exhausted by the classical solution due to Larry
Ford with an extremely flat potential which doesn't feel the fast roll of its
argument. And, moreover, one needs to fulfil an extra condition on that
potential in order to avoid severe gradient instability. At the same time, some
Lorentz-violating modifications are worth to be explored.
