The real singlet scalar dark matter model (1006.2518v3)

Abstract: We present an undated comprehensive analysis for the simplest dark matter model in which a real singlet scalar with a $Z_2$ symmetry is introduced to extend the standard model. According to the observed dark matter abundance, we predict the dark matter direct and indirect detection cross sections for the whole parameter space. The Breit-Wigner resonance effect has been considered to calculate the thermally averaged annihilation cross section. It is found that three regions can be excluded by the current direct and indirect dark matter search experiments. In addition, we also discuss the implication of this model for the Higgs searches at colliders.

The Real Singlet Scalar Dark Matter Model

The real singlet scalar dark matter (DM) model analyzed by Guo and Wu presents a minimal extension to the standard model (SM) by introducing a real singlet scalar particle. This model is characterized by its simplicity, maintaining a discrete $Z_2$ symmetry which stabilizes the dark matter candidate. The focus of the paper is on the model's predictive accuracy concerning observed dark matter abundance, which sets constraints on the DM-Higgs coupling, influencing both the direct and indirect detection rates of dark matter and the implications for Higgs physics at colliders.

Model Features and Stability

The model introduces a single scalar field $S$, requiring the application of a $Z_2$ symmetry ($S \rightarrow -S$), ensuring stability without a non-zero vacuum expectation value. The scalar potential includes a quartic term, with the DM mass $m_D$ derived from parameters dependent on the electroweak symmetry breaking scale. The authors evaluate the parameter space for dark matter and Higgs masses, optimizing calculations for $10 \; {\rm GeV} \leq m_D \leq 200$ GeV, while the Higgs mass $m_h$ varies according to established constraints from collider data and precision electroweak measurements.

Annihilation Cross Sections and Relic Density

The paper extensively discusses the DM annihilation channels, accounting for fermion pair production, gauge boson pairs, and Higgs pairs, enabling the calculation of annihilation cross sections. The Breit-Wigner resonance effect is specifically addressed for scenarios where the DM particle mass approaches half the Higgs boson mass. This effect is pivotal, substantially affecting the thermally averaged annihilation cross section $\langle \sigma v \rangle$, which in turn influences relic abundance predictions and coupling constraints. Numerical evaluations indicate that $\lambda$, the DM-Higgs coupling, spans several orders of magnitude based on $m_D$ and $m_h$ values, with resonance contributions causing significant deviations from expected parameters if the Breit-Wigner effect is neglected.

Direct and Indirect Detection Constraints

In assessing the implications for DM direct detection, the authors determine the DM-nucleon elastic scattering cross section $\sigma_{n}^{SI}$. They find that current experiments, such as CDMS II and XENON10, provide exclusion regions within the parameter space and predict potential sensitivities for future searches. The resonance region presents particular challenges for detection due to reduced interaction cross sections, highlighting the importance of continued experimental sensitivity improvements.

For indirect searches, the thermally averaged cross section is assessed at current galactic velocities to determine DM annihilation rates, accounting for enhancements or suppressions influenced by the Breit-Wigner effect. While the PAMELA antiproton data provides some constraints, the authors note that much of the parameter space remains accessible to future experiments like AMS-02, particularly in scenarios not heavily affected by the resonance effect.

Implications for Higgs Physics

The model predicts notable consequences for Higgs searches, with invisible Higgs decays ($h \rightarrow SS$) introducing a novel signature in high-energy colliders such as the LHC. This decay diminishes the visible decay branching ratio of the Higgs, necessitating combined analyses of both visible and invisible decay rates for comprehensive searches. The paper meticulously outlines conditions under which the real singlet scalar model remains viable given experimental data, illustrating a potential overlap with regions of parameter space consistent with current collider constraints.

Conclusion

Guo and Wu's comprehensive analysis of the real singlet scalar dark matter model offers significant insights into the interplay between dark matter phenomenology and Higgs physics, underscoring the model's predictability and constraints. While ensuring compatibility with observed dark matter abundance, the model maintains potential for addressing anomalies and extending collider search strategies. Future experimental data will be crucial in refining these predictions and assessing the model's viability in the broader context of particle physics and cosmology.