Global analyses of Higgs portal singlet dark matter models using GAMBIT (1808.10465v3)

Abstract: We present global analyses of effective Higgs portal dark matter models in the frequentist and Bayesian statistical frameworks. Complementing earlier studies of the scalar Higgs portal, we use GAMBIT to determine the preferred mass and coupling ranges for models with vector, Majorana and Dirac fermion dark matter. We also assess the relative plausibility of all four models using Bayesian model comparison. Our analysis includes up-to-date likelihood functions for the dark matter relic density, invisible Higgs decays, and direct and indirect searches for weakly-interacting dark matter including the latest XENON1T data. We also account for important uncertainties arising from the local density and velocity distribution of dark matter, nuclear matrix elements relevant to direct detection, and Standard Model masses and couplings. In all Higgs portal models, we find parameter regions that can explain all of dark matter and give a good fit to all data. The case of vector dark matter requires the most tuning and is therefore slightly disfavoured from a Bayesian point of view. In the case of fermionic dark matter, we find a strong preference for including a CP-violating phase that allows suppression of constraints from direct detection experiments, with odds in favour of CP violation of the order of 100:1. Finally, we present DDCalc 2.0.0, a tool for calculating direct detection observables and likelihoods for arbitrary non-relativistic effective operators.

• The paper demonstrates a global fitting approach using Bayesian and frequentist frameworks to analyze Higgs portal singlet dark matter models.
• It identifies viable parameter regions for scalar, vector, and fermionic DM candidates by integrating constraints from relic density, invisible Higgs decays, and direct detection experiments.
• The study highlights theoretical implications such as a preference for CP violation in fermion models and tuning challenges in vector models.

Analysis of Higgs Portal Singlet Dark Matter Models via GAMBIT

The paper presents a comprehensive investigation into the viability and parameter constraints of various Higgs portal singlet dark matter (DM) models using the global fitting framework GAMBIT. The authors explore an ensemble of models where scalar, vector, Majorana, and Dirac fermions serve as potential DM candidates, engaging through the Higgs portal—a scalar field mediator interacting with Standard Model (SM) particles. Through Bayesian and frequentist statistical methodologies, the parameters of these models are scrutinized against the latest experimental and theoretical data, including relic density constraints, invisible Higgs decays, direct detection experiments such as XENON1T, and indirect detection indicators, notably from gamma-ray searches by Fermi-LAT.

Numerical and Statistical Approaches

The analyses leverage cutting-edge statistical methods, allowing for both the frequentist and Bayesian examination of the given models. The use of GAMBIT facilitates the incorporation of diverse and up-to-date datasets into the global fit, thus enabling the determination of preferred DM mass and coupling parameters. One pivotal result is the delineation of parameter regions where the DM candidate alone can account for the entirety of the DM content in the universe. Intriguingly, the work also executes a Bayesian model comparison, which yields insight into the relative plausibility of the Higgs portal models, suggesting slight disfavor towards vector DM due to greater tuning needs.

Parameter Constraints and Findings

The extensive analysis reveals certain key findings:

• The models permit viable parameter spaces capable of explaining the full DM continuum, yet these exist under varied constraints driven by the different types of Higgs portal couplings—Higgs portal couplings that appear promising need to finely balance annihilation and interaction rates with observational limits.
• The scalar DM models remain deeply constrained by relic density and direct detection data, while fermionic models suggest a preference towards CP-violating interactions to evade direct detection bounds effectively.
• The performance of the models against observational data leads to the intriguing discovery that regions where the vector and fermion models diverge are largely dictated by the necessity for portal couplings to remain consistent with non-observation constraints from terrestrial experiments and relic abundance levels.

Theoretical and Practical Implications

The research lays fundamental parameters for future explorations and experiments seeking DM signals. The constraints highlighted offer not only guidance for experimental DM searches but also outline the theoretical ramifications for model building within and beyond the Higgs sector. The bold inclination towards CP violation in fermion models could guide theoretical extensions that inherently predict such characteristics.

Future Prospects

These analyses anchor future theoretical endeavors in distinct signatures expected for Higgs portal DM at forthcoming experiments. As new data emerges from evolving detector technologies and cosmological surveys, the robust methodologies developed here will stand crucial in deciphering the possible DM sectors fundamentally intertwined with the Higgs field, marking a decisive step forward for new physics beyond the standard model.

In conclusion, the paper expertly navigates through extensive model parameter spaces using sophisticated statistical frameworks, producing critical insights into Higgs portal singlet DM models. Each experimental constraint sketched here not only serves as an exciting target for upcoming experimental and theoretical studies but also as a beacon for broader cosmological phenomena.