The Scale of Dark QCD

TL;DR

The paper proposes that a dark QCD sector coupled to the SM via bifundamental matter can share infrared fixed points, fixing alpha_s^* and alpha_d^* and relating Lambda_QCD to Lambda_dQCD. Below a decoupling scale M ~ TeV, the two couplings run independently to generate Lambda_QCD and Lambda_dQCD, with m_D approx 1.5 Lambda_dQCD and m_p approx 1.5 Lambda_QCD. A concrete leptogenesis-inspired mechanism using bifundamental fields yields |n_D|/n_B = 79/56 and leads to Omega_DM/Omega_B approx (79/56)*(m_D/m_p), matching the Planck value for plausible Lambda_dQCD. Phenomenology includes a spin-independent DM-nucleon cross section around 3e-40 cm^2 for M_Phi/kappa_3 ~ 1 TeV and collider signatures from Phi production at the TeV scale, offering accessible tests at the LHC and direct detection experiments.

Abstract

Most of the mass of ordinary matter has its origin from quantum chromodynamics (QCD). A similar strong dynamics, dark QCD, could exist to explain the mass origin of dark matter. Using infrared fixed points of the two gauge couplings, we provide a dynamical mechanism that relates the dark QCD confinement scale to our QCD scale, and hence provides an explanation for comparable dark baryon and proton masses. Together with a mechanism that generates equal amounts of dark baryon and ordinary baryon asymmetries in the early universe, the similarity of dark matter and ordinary matter energy densities can be naturally explained. For a large class of gauge group representations, the particles charged under both QCD and dark QCD, necessary ingredients for generating the infrared fixed points, are found to have masses at one to two TeV, which sets the scale for dark matter direct detection and novel collider signatures involving visible and dark jets.

Figures (3)

• Figure 1: An illustrative picture of the gauge coupling runnings from a UV scale to the confinement scales. Different UV boundary gauge couplings can lead to the same IRFPs. After decoupling particles charged under both groups at a scale $M$, both couplings run again below $M$ and generate compatible confinement scales $\Lambda_{\rm QCD}$ and $\Lambda_{\rm dQCD}$.
• Figure 2: The distribution of numbers of models in terms of the decoupling scale $M$, after satisfying the requirement of $1.5 < m_D/m_p < 15$. The lower limit of $M$ is related to requiring $\alpha_s^* \leq 0.1$.
• Figure 3: The ratios of the dark baryon energy density over the ordinary baryon energy density for different models in Table \ref{['tab:fixed-point-values']}. The dark lines are the ratios $\Omega_{\rm DM}/\Omega_{\rm B}$ calculated using Eq. (\ref{['eqn:DMratio']}) for different models, while the orange (grey) bands are obtained by letting the dark baryon mass vary between $1/2$ and $2$ times the estimated value, to account for the uncertainty of the nonperturbative estimation of $\Lambda_{\rm dQCD}$ (a more precise calculation could be done at Lattice Appelquist:2013ms). The green line is the measured value of $\Omega_{\rm DM}/\Omega_{\rm B}$ from the Planck Collaboration.