750 GeV dark pion: Cousin of a dark $G$-parity odd WIMP

We point out a potential common origin of the recently observed 750 GeV diphoton resonance and a weakly interacting massive particle (WIMP) candidate. In a dark QCD sector with an unbroken dark $G$ parity, the diphoton resonance could be a dark $G$-even pion, while the WIMP could be the lightest dark $G$-odd pion. Both particles are Standard Model gauge singlets and have the same decay constant. For the dark pion decay constant of around 500 GeV, both the diphoton excess at the LHC and the dark matter thermal abundance can be accommodated in our model. Our model predicts additional dark $G$-even and dark $G$-odd color-octet pions within reach of the 13 TeV LHC runs. For the $5+\overline{5}$ model, compatible with the grand unified theories, the WIMP mass is predicted to be within (613,750) GeV.

Figure 1

Dark pion masses as a function of the ${\mathbf{1}}_B^{-}$ mass after fixing the lightest $G$-even dark pion, ${\mathbf{1}}^{+}$, to be 750 GeV and $f_{\mathrm{\Pi }}=350\mathrm{GeV}$. The QCD gauge couplings are chosen to have ${\alpha }_s(1\mathrm{TeV})\approx 0.09$. We do not show the masses of additional dark pions related to the ones in this plot by complex conjugation.

Figure 2

The production cross section times branching ratio for $pp\to {\mathbf{1}}^{+}\to \gamma \gamma$ at the 13 TeV LHC, with $M_{{\mathbf{1}}^{+}}=750\mathrm{GeV}$. The $\sigma \times \mathrm{Br}$ for the 750 GeV diphoton excess is shown in the black line with $1\sigma$ (green) and $2\sigma$ (yellow) bands. We also show the rescaled $Z\gamma$ constraint from the 8 TeV results [24].

Figure 3

The blue line is our model predictions of the spin-independent scattering cross sections after satisfying the dark matter thermal relic abundance ${\mathrm{\Omega }}_c$. For the $5+\overline{5}$ model, the WIMP mass is predicted to be within (613,750) GeV. The dashed and red line is the “neutrino floor” cross section [30].

Figure 4

The same as Fig. 2 but for the $8+1+1$ model with $x=1$.