Status of the scalar singlet dark matter model (1705.07931v3)

Abstract: One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a $\mathbb{Z}_2$ symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above $\sim$1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned.

• The paper demonstrates that the scalar singlet dark matter model remains viable, identifying two key parameter regions that satisfy relic density and experimental limits.
• It employs Bayesian and frequentist approaches, integrating 13 nuisance parameters to robustly combine collider, direct detection, and astrophysical constraints.
• The study implies that next-generation experiments like XENON1T will critically probe the constrained parameter space, advancing dark matter research.

Analysis of the Scalar Singlet Dark Matter Model

The paper entitled "Status of the Scalar Singlet Dark Matter Model," authored by the GAMBIT collaboration, offers a comprehensive evaluation of the scalar singlet model as a plausible dark matter (DM) candidate. It provides insight into the current viability of this model within the framework of particle physics and cosmology, incorporating multiple experimental results and constraints.

Overview

The scalar singlet model augments the Standard Model (SM) by introducing an additional neutral scalar particle that doesn't acquire a vacuum expectation value, remaining stable owing to a $\mathbb{Z}_2$ symmetry. This simple extension hypothesizes that this new scalar particle, $S$, could be a viable dark matter constituent. The model parameters primarily include the mass of the scalar ($) and its coupling ($h$$) to the SM Higgs boson. The investigation scrutinizes a range of scalar masses, extending from low mass ($$< m_h/2$, where$m_h$ is the Higgs mass) to several TeV, to ascertain this model's consistency with observed astrophysical and collider data. ### Methodology To thoroughly evaluate this model, the authors deploy both Bayesian and frequentist statistical methods across the parameter space of the scalar singlet model. Importantly, the analysis incorporates 13 nuisance parameters associated with uncertainties in experimental data, such as nuclear matrix elements and quark masses, as well as other uncertainties crucial for calculations involving direct DM detection prospects and the relic density. The authors harness the capabilities of the GAMBIT software toolkit to seamlessly integrate various likelihoods and sampling algorithms, thus providing a robust statistical framework for the analysis. ### Key Experimental Constraints Several experimental results are integrated into this assessment: 1. **Direct Detection Experiments**: Key constraints arise from LUX, PandaX, SuperCDMS, and XENON100, which place limits on the scattering cross-section of dark matter particles with nuclei. The paper utilizes experimental data to eliminate parameter regions where the cross-section exceeds observational limits. 2. **Collider Constraints**: Limits on the invisible decay width of the Higgs boson are used, given that for$ < m_h/2$$, the Higgs can decay into scalar pairs, potentially infringing upon known decay rates.</p> <ol> <li><strong>Indirect Detection</strong>: The analysis uses gamma-ray data from the Fermi-LAT for dwarf spheroidal galaxies and neutrino data from IceCube to constrain annihilation processes. Although the scalar singlet models indirectly suggest the possibility of DM signals, these experiments set upper bounds for the annihilation cross-section.</li> <li><strong>Relic Density</strong>: The scalar relic density must not exceed the DM abundance measured by the Planck satellite, hence setting a stringent cosmological constraint.</li> </ol> <h3 class='paper-heading' id='findings-and-implications'>Findings and Implications</h3> <p>The paper concludes with the identification of two prominent regions of allowed parameter space. A small region exists where$$%%%%3%%%%m_h/2$, with small couplings, allowing scalars to potentially account for the full relic density. The other region covers higher masses up to several TeV, with stronger couplings. However, points where the scalar contributes entirely to the DM relic density are marked by fine-tuning and are primarily constrained by direct detection experiments.

The analysis reveals that while the scalar singlet model remains viable, the parameter space is tightly constrained. The sensitivity of future experiments like XENON1T could further close in on these parameter regions. Importantly, the exploration of vacuum stability in the scalar singlet model indicates that it can alleviate the instability of the electroweak vacuum if the couplings are appropriately chosen, though this introduces questions of perturbativity.

Overall, the scalar singlet model serves as a key test case against which to measure the evolution and refinement of experimental techniques and understanding in DM research. The methodology and framework presented here are pertinent for future analyses seeking to interlink theoretical models with experimental progress, potentially expanding beyond the scalar singlet scenario.

Future Prospects

Building upon this paper, future work could explore more complex dark matter models, address open questions on vacuum stability with robust renormalization treatments, and expand the experimental dataset to incorporate the next generation of particle physics experiments. As our theoretical models grow more sophisticated, leveraging integrated frameworks such as GAMBIT will be pivotal in navigating the ever-expanding landscape of particle physics and cosmology research.