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Can WIMP Dark Matter overcome the Nightmare Scenario?

Shinya Kanemura, Shigeki Matsumoto, Takehiro Nabeshima, Nobuchika Okada

TL;DR

The paper examines whether a Higgs-portal SM-singlet WIMP can rescue the so-called nightmare scenario by tying dark matter to observable SM phenomena. It constructs scalar, fermion, and vector Higgs-portal candidates, computes their thermal relic densities via the Boltzmann equation, and confronts direct-detection constraints using nucleon matrix elements and current experiments. It then analyzes LHC signatures: invisible Higgs decays for m_DM < m_h/2 and off-shell Higgs–mediated DM production in vector-boson fusion for m_DM ≥ m_h/2, identifying regions testable with current or near-future data. The study finds substantial portions of the WMAP-compatible parameter space are constrained by direct detection, but complementary collider probes can still reveal Higgs-portal DM even if the broader new-physics sector remains elusive.

Abstract

Even if new physics beyond the Standard Model (SM) indeed exists, the energy scale of new physics might be beyond the reach at the Large Hadron Collider (LHC) and the LHC could find only the Higgs boson but nothing else. This is the so-called "nightmare scenario". On the other hand, the existence of the dark matter has been established from various observations. One of the promising candidates for thermal relic dark matter is a stable and electric charge-neutral Weakly Interacting Massive Particle (WIMP) with the mass below the TeV scale. In the nightmare scenario, we introduce a WIMP dark matter singlet under the SM gauge group, which only couples to the Higgs doublet at the lowest order, and investigate a possibility that such WIMP dark matter can be a clue to overcome the nightmare scenario via various phenomenological tests such as the dark matter relic abundance, the direct detection experiments for the dark matter particle, and the production of the dark matter particle at the LHC.

Can WIMP Dark Matter overcome the Nightmare Scenario?

TL;DR

The paper examines whether a Higgs-portal SM-singlet WIMP can rescue the so-called nightmare scenario by tying dark matter to observable SM phenomena. It constructs scalar, fermion, and vector Higgs-portal candidates, computes their thermal relic densities via the Boltzmann equation, and confronts direct-detection constraints using nucleon matrix elements and current experiments. It then analyzes LHC signatures: invisible Higgs decays for m_DM < m_h/2 and off-shell Higgs–mediated DM production in vector-boson fusion for m_DM ≥ m_h/2, identifying regions testable with current or near-future data. The study finds substantial portions of the WMAP-compatible parameter space are constrained by direct detection, but complementary collider probes can still reveal Higgs-portal DM even if the broader new-physics sector remains elusive.

Abstract

Even if new physics beyond the Standard Model (SM) indeed exists, the energy scale of new physics might be beyond the reach at the Large Hadron Collider (LHC) and the LHC could find only the Higgs boson but nothing else. This is the so-called "nightmare scenario". On the other hand, the existence of the dark matter has been established from various observations. One of the promising candidates for thermal relic dark matter is a stable and electric charge-neutral Weakly Interacting Massive Particle (WIMP) with the mass below the TeV scale. In the nightmare scenario, we introduce a WIMP dark matter singlet under the SM gauge group, which only couples to the Higgs doublet at the lowest order, and investigate a possibility that such WIMP dark matter can be a clue to overcome the nightmare scenario via various phenomenological tests such as the dark matter relic abundance, the direct detection experiments for the dark matter particle, and the production of the dark matter particle at the LHC.

Paper Structure

This paper contains 9 sections, 10 equations, 3 figures.

Table of Contents

  1. Introduction
  2. The Model
  3. Cosmological Aspects
  4. Relic abundance of dark matter
  5. Direct detection of dark matter
  6. Signals at the LHC
  7. The case $m_{\rm DM} < m_h/2$
  8. The case $m_{\rm DM} \geq m_h/2$
  9. Summary and Discussions

Figures (3)

  • Figure 1: Feynman diagrams for dark matter annihilation.
  • Figure 2: Constraints on the nightmare scenario from WMAP, Xenon100 first data, and CDMS II experiments. Higgs mass is fixed to be 120 GeV in left three figures, while 150 GeV in right three figures. Expected sensitivities to detect the signal of the dark matter at XMASS, SuperCDMS, Xenon100, and LHC experiments are also shown in these figures. See the text for the detail of the region painted by dark syan (light gray).
  • Figure 3: Cross section of the dark matter signal at the LHC with and without kinematical cuts in Eq.(\ref{['kinematical cuts']}). The parameter $m_h$ and $c_{\rm DM}$ are fixed as shown in these figures.