Constraints on Scalar Dark Matter from Direct Experimental Searches

TL;DR

The paper investigates whether a Higgs-portal real scalar dark matter candidate (the darkon) can satisfy both relic-density and direct-detection constraints. In the SM+D, XENON10 and CDMS II exclude significant darkon mass ranges for given Higgs masses, motivating an extension to THDM II+D where cancellations in the Higgs-nucleon coupling suppress the darkon-nucleon cross section for certain $\tan\alpha\tan\beta$. The THDM II+D framework permits viable darkon masses around $m_D\sim(50-70)$ GeV and predicts large invisible Higgs decays $h\to DD$, potentially altering LHC Higgs signals. The work provides explicit formulas for the Higgs-nucleon coupling, darkon annihilation, and direct-detection cross sections in both models, and discusses collider implications and future experimental tests. Overall, it shows that Higgs-portal dark matter can evade current direct-detection bounds while remaining testable via Higgs phenomenology and next-generation DM searches.

Abstract

The standard model (SM) plus a real gauge-singlet scalar field dubbed darkon (SM+D) is the simplest model possessing a weakly interacting massive particle (WIMP) dark-matter candidate. The upper limits for the WIMP-nucleon elastic cross-section as a function of WIMP mass from the recent XENON10 and CDMS-II experiments rule out darkon mass ranges from 10 to (50,70,75) GeV for Higgs-boson masses of (120,200,350) GeV, respectively. This may exclude the possibility of the darkon providing an explanation for the gamma-ray excess observed in the EGRET data. We show that by extending the SM+D to a two-Higgs-doublet model plus a darkon the experimental constraints on the WIMP-nucleon interactions can be circumvented due to suppression occurring at some values of the product tan(alpha)tan(beta), with alpha being the neutral-Higgs mixing angle and tan(beta) the ratio of vacuum expectation values of the Higgs doublets. We also comment on the implication of the darkon model for Higgs searches at the LHC.

Figures (8)

• Figure 1: Current and projected upper limits for the spin-independent WIMP-nucleon elastic scattering cross-section as functions of WIMP mass. Plot courtesy of Ref. dmplot.
• Figure 2: Ranges of $x_f^{}$ and $\langle\sigma_{\rm ann}^{}v_{\rm rel}^{}\rangle$ as functions of WIMP mass $m_D$ corresponding to the 90% C.L. range $0.092\le\Omega_D^{}h^2\le0.118$.
• Figure 3: Darkon-Higgs coupling $\lambda$ in the SM+D as a function of darkon mass $m_D^{}$ for Higgs mass values $m_h^{}=120,200,350$ GeV.
• Figure 4: Darkon-nucleon elastic cross-section $\sigma_{\rm el}^{}$ in the SM+D as a function of darkon mass $m_D^{}$ for Higgs mass values $m_h^{}=120,200,350$ GeV, compared to 90% C.L. upper limits from XENON10 (black dashed-curve) and CDMS II (gray [brown] dashed-curve).
• Figure 5: Darkon-Higgs coupling $\lambda_h^{}$ in the THDM II+D as a function of darkon mass $m_D^{}$ for Higgs mass values $m_h^{}=120,200,350$ GeV and two cases with different $\tan\alpha$ and $\tan\beta$ values satisfying $\tan\alpha\,\tan\beta=0.45$. Only regions corresponding to $\lambda_h^{}<1$ have been plotted.