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.

Figure 1

The Feynman diagram of $X(750)$ production and decay at the LHC in the model.

Figure 2

Diphoton rate in our model plotted in the $M\text{−}y$ plane. The color scheme is described in the plot.