A Thermal Relic Encyclopedia: Dark Matter Candidates Coupled to Quarks

TL;DR

This work reevaluates thermal freeze-out dark matter candidates in a broad class of simplified models where the dark sector couples to Standard Model quarks via a spin-0 or spin-1 mediator. It provides a comprehensive, encyclopedia-like catalog of matrix elements, cross sections, decay rates, and the formalism needed to compute the relic density, cosmological limits, direct and indirect detection signals, collider bounds, and rare meson decays. The authors solve the Boltzmann equation to relate ⟨σv⟩ to the observed relic density Ω_DM h^2 ≈ 0.12, while applying Planck N_eff bounds, LZ direct-detection limits, Fermi- and AMS-based indirect constraints, and collider and meson-decay searches across the full m_chi–m_mediator plane. Overall, many quark-coupled thermal-relic scenarios are highly constrained, especially spin-0 mediators with scalar couplings and spin-1 mediators with vector couplings, yet sizeable viable regions remain, including scenarios with suppressed direct-detection signals or secluded annihilation channels; the results provide a practical, reference framework for future dark matter phenomenology in this class of models.

Abstract

Thermal freeze-out is a compelling framework for naturally generating the dark matter abundance. We systematically study a broad range of dark matter and mediator particle combinations that can viably realize thermal freeze-out, focusing on models in which the mediator couples to Standard Model quarks. In each case, we calculate the relic density and consider existing constraints from accelerators, cosmology, direct detection, and indirect detection over the full range of dark matter and mediator masses. We present an encyclopedic catalog of matrix elements, cross sections, and decay rates which can be used as a reference for future studies of dark matter phenomenology.

Figures (24)

• Figure 1: Results for the case of spin-0 dark matter with a spin-0 mediator that couples to up quarks. The top and bottom frames correspond to scalar and pseudoscalar couplings, respectively. The left, center, and right frames show results for mediator couplings that are maximal to quarks, equal to dark matter and quarks, and maximal to dark matter, respectively. In each case, we set the product of these two couplings to obtain a thermal relic abundance that is equal to the measured dark matter density. The meanings of the various colored regions are summarized in Sec. \ref{['sec:result']} and the model is described in Sec. \ref{['sec:Dm0Med0']}. The viable regions of parameter space are shown in white (and in white with black dots). See Table \ref{['tab:summary']} for links to other figures.
• Figure 2: As in Fig. \ref{['fig:u_6_panel']}, but for spin-0 dark matter with a spin-0 mediator that couples to down quarks, for scalar or pseudoscalar couplings. The meanings of the various colored regions are summarized in Sec. \ref{['sec:result']} and the model is described in Sec. \ref{['sec:Dm0Med0']}. The viable regions of parameter space are shown in white (and in white with black dots). See Table \ref{['tab:summary']} for links to other figures.
• Figure 3: As in Fig. \ref{['fig:u_6_panel']}, but for spin-0 dark matter with a spin-0 mediator that couples to charm quarks, for scalar or pseudoscalar couplings. The meanings of the various colored regions are summarized in Sec. \ref{['sec:result']} and the model is described in Sec. \ref{['sec:Dm0Med0']}. The viable regions of parameter space are shown in white (and in white with black dots). See Table \ref{['tab:summary']} for links to other figures.
• Figure 4: As in Fig. \ref{['fig:u_6_panel']}, but for spin-0 dark matter with a spin-0 mediator that couples to strange quarks, for scalar or pseudoscalar couplings. The meanings of the various colored regions are summarized in Sec. \ref{['sec:result']} and the model is described in Sec. \ref{['sec:Dm0Med0']}. The viable regions of parameter space are shown in white (and in white with black dots). See Table \ref{['tab:summary']} for links to other figures.
• Figure 5: As in Fig. \ref{['fig:u_6_panel']}, but for spin-0 dark matter with a spin-0 mediator that couples to bottom quarks, for scalar or pseudoscalar couplings. The meanings of the various colored regions are summarized in Sec. \ref{['sec:result']} and the model is described in Sec. \ref{['sec:Dm0Med0']}. The viable regions of parameter space are shown in white (and in white with black dots). See Table \ref{['tab:summary']} for links to other figures.