  This work is an analytical study of the main differences between classical
inflationary effects of a fast-roll regime and imprints of hybrid Loop Quantum
Cosmology (LQC) on the primordial power spectrum. Effective LQC solutions of
phenomenological interest typically contain a classical period of kinetic
dominance prior to slow-roll inflation, with consequences on the power spectrum
that here we try and tell apart from those of phenomena occuring in the
vicinity of a bounce in hybrid LQC. For this comparison, we use the same
criterion for the choice of a vacuum state of the primordial perturbations,
both in the context of relativistic cosmology and on the LQC cosmological
background. As a first approximation to the problem, our study ignores the
influence of a quasi-de Sitter evolution (rather than de Sitter) in the
slow-roll inflationary regime, and of a typically short transition between the
kinetically dominated era and the slow-roll period. Our results show that,
while the two studied types of effects can lead to a drastic power suppression
in the infrared sector of the spectrum, the mode scale at which this happens is
much larger for LQC than for classical relativistic cosmology, the
corresponding scales being related to the spacetime curvature at the bounce and
at the onset of inflation, respectively.
