Non-Abelian Dark Sectors and Their Collider Signatures

TL;DR

The work addresses astrophysical hints for dark matter by positing a non-Abelian dark sector broken at the GeV scale, connected to the SM through kinetic mixing. It develops concrete dark-Higgs sectors, analyzes mass splittings that realize XDM/iDM, and explores SUSY-related mechanisms to generate the GeV scale. The authors provide benchmark non-SUSY and SUSY models and perform a model-independent collider-phenomenology study, highlighting lepton jets, displaced vertices, and rare Z decays as key signatures at the Tevatron and LHC, with a novel method to measure the MSSM LSP mass. Overall, the paper demonstrates a rich set of collider observables that could reveal a hidden non-Abelian dark sector and its interplay with supersymmetry.

Abstract

Motivated by the recent proliferation of observed astrophysical anomalies, Arkani-Hamed et al. have proposed a model in which dark matter is charged under a non-abelian "dark" gauge symmetry that is broken at ~ 1 GeV. In this paper, we present a survey of concrete models realizing such a scenario, followed by a largely model-independent study of collider phenomenology relevant to the Tevatron and the LHC. We address some model building issues that are easily surmounted to accommodate the astrophysics. While SUSY is not necessary, we argue that it is theoretically well-motivated because the GeV scale is automatically generated. Specifically, we propose a novel mechanism by which mixed D-terms in the dark sector induce either SUSY breaking or a super-Higgs mechanism precisely at a GeV. Furthermore, we elaborate on the original proposal of Arkani-Hamed et al. in which the dark matter acts as a messenger of gauge mediation to the dark sector. In our collider analysis we present cross-sections for dominant production channels and lifetime estimates for primary decay modes. We find that dark gauge bosons can be produced at the Tevatron and the LHC, either through a process analogous to prompt photon production or through a rare Z decay channel. Dark gauge bosons will decay back to the SM via "lepton jets" which typically contain >2 and as many as 8 leptons, significantly improving their discovery potential. Since SUSY decays from the MSSM will eventually cascade down to these lepton jets, the discovery potential for direct electroweak-ino production may also be improved. Exploiting the unique kinematics, we find that it is possible to reconstruct the mass of the MSSM LSP. We also present decay channels with displaced vertices and multiple leptons with partially correlated impact parameters.

Figures (25)

• Figure 1: A schematic illustration of the minimal setup we consider in this paper. The dark sector and the SM are connected through kinetic mixing term suppressed by $\epsilon \lesssim 10^{-3}$. The dark matter multiplet may or may not couple directly to the SM. Supersymmetric extensions of this scenario are also discussed.
• Figure 2: The ratio of the XDM splitting to the iDM splitting as a function of triplet dark matter $U(1)_y$ hypercharge. The green horizontal line indicates the minimum ratio for simultaneously achieving both splittings. Red (line) is an example of two Higgs doublets with charge preserved, blue (dashed) represents two Higgs doublets with charge broken, and black (dots) adds a Higgs triplet to the previous case. For this example, the gauge couplings are $g=0.97$ and $g_y=0.26$, and in terms of Eq. \ref{['eqn:2HDPot']} we have for all three models $v_1=0.9 \; \mathrm {GeV}$, $v_2=1.1 \; \mathrm {GeV}$ and $\lambda_{1,2,3,4} = 1$. Red (line) and black (dots) add charge breaking with $\cos \alpha = 0.75$, and for black (dots), in terms of Eq. \ref{['eqn:2D1TP']}, $\lambda_\Phi=1$, $v_\Phi = 1 \; \mathrm {GeV}$ and the triplet is decoupled from the doublets at tree-level by imposing the discrete symmetry: $\Phi \rightarrow - \Phi$.
• Figure 3: Two contour plots of the ratio of the XDM splitting to the iDM splitting for triplet dark matter with two Higgs doublets and one Higgs triplet. The shaded regions represent splitting ratios where XDM and iDM can be achieved simultaneously. In both plots, the horizontal axis is the dark matter $U(1)_y$ hypercharge. The vertical axis of the left plot represents the ratio of the triplet to doublet VEVs, $v_\Phi / v$, where $v^2=v_u^2+v_d^2$ and $\left< \Phi\right> = v_\Phi T_3$. The vertical axis of the right plot represents the ratio of dark hypercharge and $SU(2)$ couplings, $g' / g$. For both plots, the triplet is decoupled from the doublets at tree-level by imposing the discrete symmetry: $\Phi \rightarrow - \Phi$, and in terms of Eq. \ref{['eqn:2HDPot']} we have $v_1=0.9 \; \mathrm {GeV}$, $v_2=1.1 \; \mathrm {GeV}$, $\cos \alpha = 0.9$ and $\lambda_{1,2,3,4} = 1$. For the left plot, the gauge couplings are $g=0.97$ and $g_y=0.26$. For the right plot, we have also chosen, in terms of Eq. \ref{['eqn:2D1TP']}, $\lambda_\Phi$ = 1 and $v_\Phi = 1 \; \mathrm {GeV}$.
• Figure 4: The resulting spectrum for a Dirac doublet with majoron coupling.
• Figure 5: The spectrum of Non-SUSY 1, our two doublet non-SUSY benchmark. The left side shows the radiative mass splittings of the components of the dark matter triplet, measured from the ground state. The splittings allow for the XDM and iDM explanations of INTEGRAL and DAMA, respectively. The right side displays the spectrum of the GeV-scale dark sector. The $b$ fractions of the gauge bosons are indicated and determine how strongly each gauge boson couples to Standard Model electromagnetic current. Because of custodial $SU(2)$, two of the gauge bosons are degenerate and do not mix with the $b$ at tree-level, and these are the gauge bosons that couple between different dark matter states. They do mix with the $b$ at one-loop, inducing a suppressed iDM coupling, and we include the dimension 6 operators $c^T_1 | h_1 D h_1 |^2$ and $c^T_2 | h_2 D h_2 |^2$ in order to parametrize custodial breaking corrections. The parameters of this benchmark are listed in the text.