Dark matter stability without new symmetries

The stability of dark matter is normally achieved by imposing extra symmetries beyond those of the Standard Model of particle physics. In this paper we present a framework where the dark matter stability emerges as a consequence of the Standard Model symmetries. The dark matter particle is an antisymmetric tensor field (analogous to the one used for spin-1 mesons in QCD), singlet under the Standard Model gauge group. The Lagrangian possesses an accidental $Z_2$ symmetry which makes the dark matter stable on cosmological time scales. Interactions with the Standard Model fields proceed through the Higgs portal, which allows the observed dark matter abundance to be generated via thermal freeze-out. We also discuss the prospects for observing this dark matter particle in direct detection experiments.

Figure 1

Feynman diagrams contributing to the annihilation of antisymmetric tensor dark matter particles into Standard Model particles.

Figure 2

Thermally averaged annihilation cross section as a function of the dark matter mass $m_{\mathcal{B}}$ at the temperature $T=m_{\mathcal{B}}/25$, assuming $c_{\mathcal{B}}=0.1$. We also show for reference the typical cross section at freeze-out required to reproduce the correct dark matter abundance, $⟨\sigma v⟩=3\times 10^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$.

Figure 3

Value of the coupling $c_{\mathcal{B}}$ as a function of the dark matter mass that reproduces the dark matter abundance ${\mathrm{\Omega }}_{\mathcal{B}}{h}^2=0.1199\pm 0.0027$ via thermal freeze-out.

Figure 4

Spin-independent scattering cross section of dark matter particles off protons, under the assumption that the dark matter population is generated via thermal freeze-out. We also show for comparison the present upper limit from the LUX experiment, as well as the projected sensitivity of the LUX and XENON1T experiments.