A Loop-philic Pseudoscalar

We construct a weakly-coupled renormalizable model to explain the $750GeV$ diphoton excess. The $750GeV$ 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 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 to be tuned to near non-perturbative 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 $5\mathrm{/}3$ and $2\mathrm{/}3$, respectively. Rich phenomenology is expected with respect to collider searches, flavor physics and dark matter detection, if $X(750)$ can be pinned down by future LHC experiments.