The Simplest Dark-Matter Model, CDMS II Results, and Higgs Detection at LHC

TL;DR

The paper investigates how the CDMS II results constrain the simplest WIMP dark matter scenario, the SM+D, which adds a real SM-singlet scalar (the darkon) coupled to the Higgs via a Higgs-portal interaction. Relic-density calculations from Higgs-mediated annihilation set the required darkon-Higgs coupling $\lambda$, and the model predicts a DM-nucleon cross-section $\sigma_{\rm el}$ that can be tested by direct-search experiments, with specific predictions depending on $m_D$ and $m_h$. The study reveals strong correlations among $m_D$, $\sigma_{\rm el}$, $m_h$, and $BR(h\to DD)$, including resonant behavior at $m_h = 2 m_D$ and potential multiple solutions for $m_D$ for a given cross-section. The results highlight that measurements of the Higgs mass and its invisible width at the LHC can complement direct detection to pin down darkon properties, demonstrating a tightly coupled interplay between collider Higgs phenomenology and DM searches.

Abstract

The direct-search experiment for dark matter performed by the CDMS II Collaboration has observed two candidate events. Although these events cannot be interpreted as significant evidence for the presence of weakly interacting massive particle (WIMP) dark matter (DM), the total CDMS II data have led to an improved upper-limit on the WIMP-nucleon spin-independent cross-section. We study some implications of these results for the simplest WIMP DM model, the SM+D, which extends the standard model (SM) by the addition of a real SM-singlet scalar field dubbed darkon to play the role of the DM. We find that, although the CDMS II data rule out a sizable portion of parameter space of the model, a large part of the parameter space is still allowed. We obtain strong correlations among the darkon mass, darkon-nucleon cross-section, mass of the Higgs boson, and branching ratio of its invisible decay. We point out that measurements of the Higgs invisible branching-ratio at the LHC can lift some possible ambiguities in determining the darkon mass from direct DM searches.

Figures (5)

• Figure 1: Darkon-Higgs coupling $\lambda$ as a function of the darkon mass $m_D^{}$ for Higgs mass values $m_h^{}=120,170,200$ GeV. The band widths in all figures result from the relic-density range which we have taken, $0.1065\le\Omega_D^{}h^2\le0.1181$.
• Figure 2: Darkon-Higgs coupling $\lambda$ as a function of the Higgs mass $m_h^{}$ for darkon mass values $m_D^{}=60,70,100$ GeV.
• Figure 3: Darkon-nucleon elastic cross-section $\sigma_{\rm el}^{}$ as a function of the darkon mass $m_D^{}$ for Higgs mass values $m_h^{}=120,170,200$ GeV, compared to 90%-C.L. upper limits from CDMS II (dashed curve) and XENON10 (dotted curve).
• Figure 4: Darkon-nucleon elastic cross-section $\sigma_{\rm el}^{}$ as a function of the Higgs mass $m_h^{}$ for darkon mass values $m_D^{}=60,70,100$ GeV.
• Figure 5: Partial width and branching ratio of the invisible decay $h\to DD$ as functions of the darkon mass $m_D^{}$ for Higgs mass values $m_h^{}=120,170,200$ GeV.