  We develop a many-body approach to the behavior of exciton bound states and
the conduction electron band edge in a surrounding electron-hole plasma with a
focus on the absorption spectrum of Rydberg excitons in cuprous oxide. The
interplay of band edge and exciton levels is analyzed numerically, whereby the
self-consistent solution is compared to the semiclassical Debye approximation.
Our results provide criteria which allow to verify or rule out the different
band edge models against future experimental data.
