Inflationary Instabilities of Einstein-Aether Cosmology
  We examine the consequences of Lorentz violation during slow-roll inflation.
We consider a canonical scalar inflaton coupled, through its potential, to the
divergence of a fixed-norm timelike vector field, or "aether." The vector is
described by Einstein-aether theory, a vector-tensor model of gravitational
Lorentz violation. We derive and analyze the cosmological perturbation
equations for the metric, inflaton, and aether. If the scale of Lorentz
violation is sufficiently small compared to the Planck mass, and the strength
of the scalar-aether coupling is suitably large, then the spin-0 and spin-1
perturbations grow exponentially and spoil the inflationary background. The
effects of such a coupling on the CMB are too small to be visible to current or
near-future CMB experiments; unusually, no isocurvature modes are produced at
first order in a perturbative expansion around the aether norm. These results
are discussed for both a general potential and a worked example, $m^2 \phi^2$
inflation with a quadratic scalar-aether coupling term.
