Pseudoscalar Decaying Only via Loops as an Explanation for the 750 GeV Diphoton Excess.

We construct a weakly coupled renormalizable model to explain the 750 GeV diphoton excess. The 750 GeV resonance [denoted as X(750)] is interpreted as a pseudoscalar coming from a complex singlet. The model also naturally provides a dark matter candidate. One of the most attractive feature of the model is that decays of X(750) are all loop induced, so the diphoton rate is not diluted by unwanted tree level branching fractions. Relevant Yukawa interactions need not be tuned to the near-nonperturbative region to explain the rate. The model is highly predictive, including the pseudoscalar nature of X(750) and two nearly mass-degenerate exotic quarks carrying electric charge 5/3 and 2/3, respectively. Rich phenomenology is expectedf with respect to collider searches, flavor physics, and dark matter detection, if X(750) can be pinned down by future LHC experiments.