  In this work we investigate characteristic modifications of the spectrum of
cosmological perturbations and the spectral index due to chain inflation. We
find two types of effects. First, modifications of the spectral index depending
on interactions between radiation and the vacuum, and on features of the
effective vacuum potential of the underlying fundamental theory. Second, a
modulation of the spectrum signalling new physics due to bubble nucleation.
This effect is similar to those of transplanckian physics. Measurements of such
signatures could provide a wealth of information on the fundamental physics at
the basis of inflation.
