The phenomenology of trapped inflation
  Trapped inflation is a mechanism in which particle production from the moving
inflaton is the main source of friction in the inflaton equation of motion. The
produced fields source inflaton perturbations, which dominate over the vacuum
ones. We employ the set of equations for the inflaton zero mode and its
perturbations which was developed in the original work on trapped inflation,
and which we extend to second order in the perturbations. We build on this
study by updating the experimental constraints, and by replacing the existing
approximate solutions with more accurate ones. We obtain a different numerical
value for the amplitude of the scalar power spectrum, and a parametrically
different result for the bispectrum. This has implications for the allowed
region of parameter space in models of trapped inflation, and for some of the
phenomenological results obtained in this region. The main results in the
allowed region are the following: monomial inflaton potentials, such as $V
\propto \varphi ,\, \varphi^2$ can be compatible with the data, and (in a
portion of the allowed region) the inflaton can be sub-Planckian over all the
"observable" stage of inflation; gravitational waves from this mechanism are
too small to be observed in the foreseeable future; a non-gaussianity parameter
$-60 < f_{\rm NL} < -20 $ is obtained in the allowed region for exactly
equilateral configurations, with a mild dependence on the parameters of the
model and of the inflaton potential.
