Abstract
Scalar singlet dark matter is one of the simplest and most predictive realisations of the WIMP (weakly-interacting massive particle) idea. Although the model is constrained from all directions by the latest experimental data, it still has viable regions of parameter space. Another compelling aspect of scalar singlets is their ability to stabilise the electroweak vacuum. Indeed, models of scalar dark matter are not low-energy effective theories, but can be valid all the way to the Planck scale. Using the GAMBIT framework, we present the first global fit to include both the low-energy experimental constraints and the theoretical constraints from UV physics, considering models with a scalar singlet charged under either a mathbb {Z}_2 or a mathbb {Z}_3 symmetry. We show that if the model is to satisfy all experimental constraints, completely stabilise the electroweak vacuum up to high scales, and also remain perturbative to those scales, one is driven to a relatively small region of parameter space. This region has a Higgs-portal coupling slightly less than 1, a dark matter mass of 1–2 TeV and a spin-independent nuclear scattering cross-section around 10^{-45},hbox {cm}^2.
Highlights
A remarkable feature of the scalar singlet dark matter (DM) model is that, just like the Standard Model (SM), it remains valid up to very high energies – potentially up to the Planck scale MPl ∼ O(1019) GeV
Even though the expected lifetime of the electroweak vacuum state far exceeds the age of Universe, it is an appealing feature of scalar singlet models that the additional coupling between the Higgs and the scalar singlet affects the running of the Higgs quartic coupling at high scales and can prevent it from becoming negative [4,5,6,7,8,9,10,11,12,13,14]
In this work we have investigated two realisations of scalar singlet DM: a real scalar stabilised by a Z2 symmetry and a complex scalar stabilised by a Z3 symmetry
Summary
A remarkable feature of the scalar singlet DM model is that, just like the SM, it remains valid up to very high energies – potentially up to the Planck scale MPl ∼ O(1019) GeV. In this work we present the most comprehensive study of scalar singlet DM to date by combining the information from low-energy observables, such as the relic abundance of scalar singlets and experimental constraints, with a study of the properties of the model at high energies, in particular perturbativity and vacuum stability For this purpose we use the GAMBIT global fitting package [15], which enables the user to incorporate existing software via a backend system. Perturbativity, vacuum stability, direct detection and the relic density of scalar singlets with a Z3 symmetry have been investigated [8,49] The latter case introduces new phenomenology due to an additional cubic S coupling, leading to semi-annihilations. GAMBIT software can be downloaded from http://gambit. hepforge.org, and all samples, input files and best-fit points from this paper are available from Zenodo [57]
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