Can WIMP Dark Matter overcome the Nightmare Scenario? (1005.5651v1)

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.

Analysis of WIMP Dark Matter in the Nightmare Scenario

The paper "Can WIMP Dark Matter overcome the Nightmare Scenario?" investigates the feasibility of using Weakly Interacting Massive Particle (WIMP) dark matter as a means to surpass the "nightmare scenario" in particle physics. This scenario arises if the Large Hadron Collider (LHC) uncovers only the Higgs boson without any evidence of new physics beyond the Standard Model (SM), possibly due to the energy scale of new physics exceeding the experimental reach of the LHC. The authors explore the hypothesis that WIMP dark matter, which remains a thermal relic with mass below the TeV scale and exhibits minimal interaction with SM particles, could provide insights into new physics despite the nightmare scenario.

Model and Theoretical Framework

The paper extends the SM by introducing WIMP dark matter as a singlet under the SM gauge group. The singlet nature ensures the dark matter is not easily observable through weak interactions with SM gauge bosons, thus constituting a "worst-case" scenario. The framework incorporates three forms of WIMP dark matter: scalar, fermionic, and vector, each interacting with SM particles primarily via the Higgs boson. This interaction paradigm, the "Higgs portal," retains the stability and non-observability of dark matter via a global $Z_2$ symmetry.

Cosmological Implications

The relic abundance and direct detection potential of WIMP dark matter serve as essential phenomenological tests for the model. Utilizing the WMAP experiment's results, the authors derive parameter regions that satisfy observational constraints on dark matter density. These calculations employ the Boltzmann equation to model thermodynamic properties of the early universe, yielding relic abundance consistent with the $\Lambda$CDM cosmological model. Furthermore, direct detection experiments such as CDMS II and XENON100 impose severe constraints on the dark matter-nucleon scattering cross-sections, eliminating most parameter space for light dark matter masses. Upcoming experiments, including SuperCDMS and XMASS, are expected to explore additional regions of this parameter space.

Collider Phenomenology

In terms of collider signals at the LHC, the paper examines scenarios where the dark matter mass is less than half the Higgs boson mass, leading to significant invisible decay branching ratios of the Higgs. Such decay processes can potentially be identified via weak gauge boson fusion mechanisms, where corresponding kinematic signatures are thoroughly analyzed. At the collider, the authors demonstrate the potential utility of signal analysis to detect dark matter produced in association with Higgs bosons, presenting feasibility studies for detection within current and future LHC operations. The research underscores the challenges and limitations of conventional detection strategies for cases where dark matter exceeds this mass threshold, while suggesting enhanced detection tactics might render these scenarios viable.

Implications for Future Research

The paper's exploration highlights the inherent complexity in overcoming the nightmare scenario using WIMP dark matter. The coupling dynamics via the Higgs portal propose an intriguing avenue where insights into novel physics could emerge indirectly through precision measurement and detection of dark matter, even when direct evidence of new physics at higher scales eludes current experimental capabilities. Future studies can refine theoretical models and employ advanced analytical techniques to further probe the elusive nature of dark matter and its role in understanding physics beyond the SM.

Conclusion

This research offers a rigorous examination of WIMP dark matter as an indirect probe for new physics in the nightmare scenario context. By bridging cosmological and collider phenomenology, the paper underscores the critical role of comprehensive experimental and theoretical investigations to unveil the characteristics of dark matter and its implications in shaping the future trajectory of particle physics research. The paper serves as a cornerstone for ongoing efforts to reconcile SM limitations with observational enigmas, catalyzing continued investigation into the fundamental underpinnings of the universe.