  Adiabatic perturbations in the cosmology of a quintessential scalar field
with exponential potential gravitationally coupled to radiation/matter are
investigated in a gauge invariant formalism. The main question addressed in
this paper is if the inhomogenous fluctuations can be ignored as often argued
and the result is that this is not always the case. Consequences for microwave
background radiation and structure formation in the matter dominated era are
considered.

Astrophysics;High Energy Physics - Theory