Abstract
A real singlet scalar, connected to the Standard Model sector through a portal with the Higgs boson, is one of the simplest and most popular models for dark matter (DM). However, the experimental advances in direct and indirect DM searches, together with the latest results from the LHC, have ruled out vast areas of the parameter space of this scenario; and are expected to probe it completely within the next years, ruling it out if no signal is found. Motivated by the simplicity of this model, in this article we address a minimal, renormalizable extension that could evade detection, consisting of the addition of an extra real singlet scalar field in the dark sector. We analyze the physical constraints on the model and show that the new annihilation and/or coannihilation channels involving the extra singlet allow to reproduce the correct DM relic abundance while avoiding the bounds from direct and indirect searches for any DM mass above 50 GeV. We also show that, in some interesting regions of the parameter space, the extra particle can be integrated-out, leaving a “clever” effective theory (just involving the DM particle and the Higgs), that essentially reproduces the results.
Highlights
The relevant processes, illustrated in figure 1, are usually dominated by the s−channel annihilation through a Higgs boson
In order to facilitate the comparison of the model with the usual scalar Higgs portal (SHP), we have carried out a series of numerical scans, for fixed values of λ12, in the three dimensional parameter space {mS1, λ1, mS2}, searching for points where S1 is a viable candidate for dark matter
One of the most economical and explored models of dark matter (DM) is the so-called singlet-scalar Higgs portal (SHP) model. It consists of an extra singlet scalar field, which is minimally coupled to the SM through interactions with the ordinary Higgs at the renomalizable level
Summary
The relevant processes, illustrated in figure 1, are usually dominated by the s−channel annihilation through a Higgs boson (leftmost diagram of the figure). Current bounds from direct DM detection, most notably from the new results from LUX [59] and PandaX-II [60], set an upper bound on the DM-nucleon elastic scattering cross section (and on the DM coupling to the Higgs) This rules out the red area in figure 2. The blue region in figure 2 is excluded for this reason
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