Closing in on Asymmetric Dark Matter I: Model independent limits for interactions with quarks

TL;DR

The paper investigates model-independent constraints on asymmetric dark matter (ADM) by mapping DM–quark interactions to effective operators and confronting them with direct detection and LHC monojet data. It shows that for ADM in the natural mass range, heavy-mediator contact interactions to SM quarks are largely excluded, necessitating an extended hidden sector with lighter mediators or additional annihilation channels. The authors then explore light mediator portals, including scalar (Higgs-like) and pseudoscalar options, demonstrating that resonance and threshold effects can revive viable ADM parameter space despite stringent collider and direct-detection limits. The work argues that realistic ADM scenarios generically require hidden-sector structure and portal dynamics, a theme they further develop in a companion paper.

Abstract

It is argued that experimental constraints on theories of asymmetric dark matter (ADM) almost certainly require that the DM be part of a richer hidden sector of interacting states of comparable mass or lighter. A general requisite of models of ADM is that the vast majority of the symmetric component of the DM number density must be removed in order to explain the observed relationship $Ω_B\simΩ_{DM}$ via the DM asymmetry. Demanding the efficient annihilation of the symmetric component leads to a tension with experimental limits if the annihilation is directly to Standard Model (SM) degrees of freedom. A comprehensive effective operator analysis of the model independent constraints on ADM from direct detection experiments and LHC monojet searches is presented. Notably, the limits obtained essentially exclude models of ADM with mass 1GeV$\lesssim m_{DM} \lesssim$ 100GeV annihilating to SM quarks via heavy mediator states. This motivates the study of portal interactions between the dark and SM sectors mediated by light states. Resonances and threshold effects involving the new light states are shown to be important for determining the exclusion limits.

Figures (5)

• Figure 1: Limits on the scale $\Lambda$ for the effective operators from direct detection and monojets for scalar DM $\phi$ and fermion DM $\psi$, as a function of DM mass $m_{\mathrm{DM}}$. The black curve corresponds to the minimum annihilation cross-section necessary to reduce the symmetric component to $1\%$. Constraints are from Xenon100 (blue), Xenon10 (green), CDMS (cyan), CRESST (orange), DAMIC (magenta) and ATLAS $1\,{\mathrm {fb}}^{-1}$ (red, dashed) and CMS $4.67\,{\mathrm {fb}}^{-1}$ (blue, dashed) monojet searches. For $m_{\mathrm{DM}}\gtrsim\Lambda$ effective operators no longer provide a good description and can not be reliably used to calculate the relic density requirements. Moreover, the monojet limits are no longer reliable much below $\Lambda\lesssim 100$ GeV due to the experimental cuts employed by ATLAS and CMS. Viable models of ADM employing the listed effective operators must lie in the shaded parameter regions. Note that contact operators due to scalar mediators are studied for both universal couplings to quarks and $m_q$-dependent couplings. We see that, except for the operator $\frac{1}{\Lambda}\phi^\dagger\phi\overline{q}q$ around $m_{\mathrm{DM}}\approx1$ GeV, successful models of ADM involving contact operators are excluded for $1~{\rm GeV}\lesssim m_{\mathrm{DM}} \lesssim 100~{\rm GeV}$, which includes the range in which ADM is most well motivated.
• Figure 2: Limits on $\Lambda$ for operators with spin-dependent direct detection cross-sections, viable parameter regions are shaded. Constraints are from Simple (Stage 2: light purple; Combined: dark purple), CRESST (orange), ATLAS $1\,{\mathrm {fb}}^{-1}$ (red, dashed) and CMS $4.67\,{\mathrm {fb}}^{-1}$ (blue, dashed).
• Figure 3: Limits on $\Lambda$ for operators with $v$ or $q$ suppressed direct detection cross-sections, viable parameter regions are shaded. Limits are from ATLAS $1\,{\mathrm {fb}}^{-1}$ (red, dashed) and CMS $4.67\,{\mathrm {fb}}^{-1}$ (blue, dashed). The interesting ADM range $m_{\mathrm{DM}}\lesssim10$ GeV is excluded in all cases and, with the exception of the $\frac{m_q}{\Lambda^3}\overline{\psi}\gamma^5\psi\overline{q}\gamma^5q$ operator, this exclusion extends up to $m_{\mathrm{DM}}\lesssim100$ GeV.
• Figure 4: Constraints on a light scalar mediator coupling fermion DM to the visible sector via mixing with a SM-like Higgs with mass $m_h=125$ GeV. The black curve shows the minimum DM-mediator coupling $\lambda_{X}$ required to efficiently annihilate the symmetric component of the DM. The red curve indicates the current combined spin independent direct detection bounds. Constraints from monojet searches are negligible. The allowed parameter space is indicated by the shaded region. For mediators heavier than a few GeV only the resonance region survives the tension between direct detection limits and the requirement for efficient annihilation of the symmetric component.
• Figure 5: Constraints on a pseudoscalar mediator coupling fermion DM to the visible sector. The solid curve shows the required hidden sector coupling in order to efficiently annihilate the symmetric component. The dashed curve visible near 5 GeV (the resonance region) indicates the LHC monojet limits, as can be seen these do not present significant constraints on the model, this is in contrast to the corresponding contact operator $\mathcal{O}^\psi_{p}$ studied in Section \ref{['Sec3']}. Moreover, as the scattering cross-section is suppressed by $q^4$ there are essentially no limits from direct detection. The allowed parameter space is indicated by the shaded region.