Tachyonic Preheating in Plateau Inflation
  Plateau inflation is an experimentally consistent framework in which the
scale of inflation can be kept relatively low. Close to the edge of the
plateau, scalar perturbations are subject to a strong tachyonic instability.
Tachyonic preheating is realized when, after inflation, the oscillating
inflaton repeatedly re-enters the plateau. We develop the analytic theory of
this process and expand the linear approach by including backreaction between
the coherent background and growing perturbations. For a family of plateau
models, the analytic predictions are confronted with numerical estimates. Our
analysis shows that the inflaton fragments in a fraction of an $e$-fold in all
examples supporting tachyonic preheating, generalizing the results of previous
similar studies. In these scenarios, the scalar-to-tensor ratio is tiny,
$r<10^{-7}$.
