  Interactions between the inflaton and any additional fields can lead to
isolated bursts of particle production during inflation (for example from
parametric resonance or a phase transition). Inflationary particle production
leaves localized features in the spectrum and bispectrum of the observable
cosmological fluctuations, via the Infra-Red (IR) cascading mechanism. We focus
on a simple prototype interaction g^2 (\phi-\phi_0)^2\chi^2 between the
inflaton, \phi, and iso-inflaton, \chi; extending previous work on this model
in two directions. First, we quantify the magnitude of the produced
nongaussianity by extracting the moments of the probability distribution
function from lattice field theory simulations. We argue that the bispectrum
feature from particle production might be observable for reasonable values of
the coupling, g^2. Second, we develop a detailed analytical theory of particle
production and IR cascading during inflation, which is in excellent agreement
with numerical simulations. Our formalism improves significantly on previous
approaches by consistently incorporating both the expansion of the universe and
also metric perturbations. We use this new formalism to estimate the shape of
the bispectrum from particle production, showing this to be distinguishable
from other mechanisms that predict large nongaussianity.
