Diphoton and diboson excesses in a left-right symmetric theory of dark matter

We explore the possibility that the recently reported diphoton excess at ATLAS and CMS can be accommodated within a minimal extension of a left-right symmetric model. Our setup is able to simultaneously explain the Run 2 diphoton and Run 1 diboson excesses, while providing a standard thermal freeze-out of weak-scale dark matter. In this scenario, the 750 GeV neutral right-handed Higgs triplet is responsible for the diphoton excess. Interactions of this state with the neutral and charged components of dark matter multiplets provide the dominant mechanisms for production and decay. A striking signature of this model is the additional presence of missing energy in the diphoton channel.

Figure 1

Production mechanism for the diphoton signal. The gray circle corresponds to a loop of charged mediators, as discussed in Sec. 3b.

Figure 2

Examples of viable parameter space for the Run 2 diphoton and Run 1 diboson signals. $m_{W^{\prime }}$, $g_R$, and $\tan \beta$ are fixed to values consistent with the diboson excess. Regions favorable with the diphoton excess [$R_{\gamma \gamma }/\mathrm{BR}({\mathrm{\Delta }}^0\to \gamma \gamma )\sim \text{few}\mathrm{fb}$] are highlighted in green. Also shown is the parameter space where the relic abundance of ${\chi }_1$ matches the observed dark matter density (black).

Figure 3

The branching fraction of ${\mathrm{\Delta }}^0\to \gamma \gamma$ for the set of parameters corresponding to the bottom-right panel of Fig. 2. For $M_{23}\lesssim 400\mathrm{GeV}$, tree-level decays of ${\mathrm{\Delta }}^0$ to dark matter dominate the width. This demonstrates that these models are able to account for the Run 2 diphoton signal for $M_{23}\gtrsim 400\mathrm{GeV}$, across the green regions in Fig. 2.