  Axionlike particles (ALPs) could mix with photons in the presence of
astrophysical magnetic fields. Searching for this effect in gamma-ray
observations of blazars has provided some of the strongest constraints on ALP
parameter space so far. Previously, photon-photon dispersion of gamma-rays off
of the CMB has been shown to be important for these calculations, and is
universally included in ALP-photon mixing models. Here, we assess the effects
of dispersion off of other photon fields within the blazar (produced by the
accretion disk, the broad line region, the dust torus, starlight, and the
synchrotron field) by modelling the jet and fields of the flat spectrum radio
quasar 3C454.3 and propagating ALPs through the model both with and without the
full dispersion calculation. We find that the full dispersion calculation can
strongly affect the mixing, particularly at energies above 100 GeV -- often
reducing the ALP-photon conversion probability. This could have implications
for future searches planned with, e.g., the Cherenkov Telescope Array,
particularly those looking for a reduced opacity of the universe at the highest
energies.
