Phenomenology of dark matter in chiral ${\mathrm{U}(1)}_X$ dark sector

We consider dark matter physics in a model for the dark sector with extra dark ${\mathrm{U}(1)}_X$ gauge symmetry. The dark sector is composed of exotic fermions that are charged under both dark ${\mathrm{U}(1)}_X$ and the standard model ${\mathrm{SU}(3)}_C\times \mathrm{U}(1{)}_Y$ gauge groups, as well as standard model singlet complex scalars $\mathrm{\Phi }$ and $X$ with nonzero ${\mathrm{U}(1)}_X$ charge. In this model, there are two dark matter candidates—a scalar and a fermion—both of which are stabilized by accidental $Z_2$ symmetry. Their thermal relic density, and direct and indirect detection constraints are discussed in detail and we search for the parameter space of the model accommodating dark matter observations. We also discuss constraints from diphoton resonance searches associated with the scalar field which breaks the dark ${\mathrm{U}(1)}_X$, in a way consistent with dark matter physics. In addition, implications for collider physics are discussed, focusing on the production cross section of the scalar boson.

Figure 1

The parameter region explaining the observed relic density of DM in the $m_X\text{−}{\lambda }_{X\mathrm{\Phi }}$ and $M_N\text{−}{g}_X$ planes for scalar and fermionic DM cases, respectively, in scheme 1).

Figure 2

The left (right) plot shows the parameter region explaining the observed relic density of DM in the $g_X\text{−}{m}_X$ (${\lambda }_{X\mathrm{\Phi }}\text{−}{m}_X$) plane for scalar DM in scheme 2).

Figure 3

The parameter region explaining the observed relic density of DM in the $g_X\text{−}{M}_N$ plane for fermion DM in scheme 2).

Figure 4

The DM-nucleon scattering cross section as a function of DM mass for scheme 1) where the parameters satisfying the observed relic density in Fig. 1 are applied. The left and right plots correspond to scalar and fermionic DM cases, respectively.

Figure 5

The DM-nucleon scattering cross section as a function of DM mass for scheme 2) where the parameters satisfying the observed relic density in Figs. 2 and 3 are applied.

Figure 6

The present-day thermally averaged cross section for $XX\to gg$ where the parameter region in Fig. 1 is applied. The black solid line indicates the current limit of the cross section for the $\mathrm{DM}\mathrm{DM}\to b\overline{b}$ annihilation mode from Fermi-LAT.

Figure 7

The present-day effective thermally averaged cross section for $⟨\sigma v{⟩}_{\mathrm{eff}}$ of Eq. (28) where the parameter region in Fig. 2 is applied. The black solid (dashed) line indicates the current limit of the cross section for the $\mathrm{DM}\mathrm{DM}\to b\overline{b}$ $(\tau \overline{\tau })$ annihilation mode from Fermi-LAT.

Figure 8

The parameter region that can accommodate the relic density of DM and constraints from collider experiments for scalar and fermion DM in scheme 1).

Figure 9

The parameter region that can accommodate the thermal relic density of DM and constraints from collider experiments for scalar DM in scheme 2).

Figure 10

The parameter region that can accommodate the relic density of DM and constraints from collider experiments for fermion DM in scheme 2).

Figure 11

The $\varphi$ production cross section for the parameter region in Fig. 8. The dotted lines indicate the upper limits on the cross section from the $pp\to \varphi \to XX$ channel with monojet search data at the LHC [64].

Figure 12

The $\varphi$ production cross section for the parameter region in Fig. 9. The dashed line indicates the upper limit on the cross section from the dijet search at the LHC [65] for $\mathrm{BR}(\varphi \to jj)=1.0$. The dotted lines in the right panel are the monojet constraints as in Fig. 11.

Figure 13

The $\varphi$ production cross section for the parameter region in Fig. 10. The dotted line indicates the monojet constraints as in Figs. 11 and 12.