The origin of the cosmic gamma-ray background in the MeV range
  There has been much debate about the origin of the diffuse $\gamma$--ray
background in the MeV range. At lower energies, AGNs and Seyfert galaxies can
explain the background, but not above $\simeq$0.3 MeV. Beyond $\sim$10 MeV
blazars appear to account for the flux observed. That leaves an unexplained gap
for which different candidates have been proposed, including annihilations of
WIMPS. One candidate are Type Ia supernovae (SNe Ia). Early studies concluded
that they were able to account for the $\gamma$--ray background in the gap,
while later work attributed a significantly lower contribution to them.
  All those estimates were based on SN Ia explosion models which did not
reflect the full 3D hydrodynamics of SNe Ia explosions. In addition, new
measurements obtained since 2010 have provided new, direct estimates of high-z
SNe Ia rates beyond $z\sim$2. We take into account these new advances to see
the predicted contribution to the gamma--ray background.
  We use here a wide variety of explosion models and a plethora of new
measurements of SNe Ia rates. SNe Ia still fall short of the observed
background. Only for a fit, which would imply $\sim$150\% systematic error in
detecting SNe Ia events, do the theoretical predictions approach the observed
fluxes. This fit is, however, at odds at the highest redshifts with recent SN
Ia rates estimates. Other astrophysical sources such as FSRQs do match the
observed flux levels in the MeV regime, while SNe Ia make up to 30--50\% of the
observed flux.
