Diphotons from Diaxions
  We study models in which the 750 GeV diphoton excess is due to a scalar decaying to two pseudo-Nambu-Goldstone bosons that subsequently decay into two pairs of highly boosted photons, misidentified as individual photons. Performing a model independent analysis we find that, with axion mass around $200$ MeV, this class of theories can naturally explain the observed signal with a large width, without violating monojet constraints. At the same time the requirement of a prompt axion decay can be satisfied only with a relatively large axion-photon coupling, leading to many new charged particles at the TeV scale. However, the required multiplicities of such fields is still moderately reduced relative to models with direct diphoton production. 
Luis Aparicio, Aleksandr Azatov, Edward Hardy and Andrea Romanino
hep-ph