  It is shown that inverse Compton gamma-rays from electrons accelerated in
large scale structure formation shocks can be crucially affected by
non-gravitational effects such as radiative cooling and galaxy formation, with
corresponding uncertainties by an order of magnitude in either the gamma-ray
source counts or the extragalactic background contribution. However, this also
implies that such gamma-rays may in the near future provide us with valuable
information about the fraction of cosmic baryons in different forms,
particularly the warm-hot intergalactic medium where the majority of the
baryons in the universe are believed to reside. We address this problem in a
simple way through semi-analytic modeling of structure formation shocks which
self-consistently treats merger and accretion shocks.
