Abstract
We consider the possibility of simultaneously addressing the dark matter problem and neutrino mass generation in the minimal inverse seesaw realisation. The Standard Model is extended by two right-handed neutrinos and three sterile fermionic states, leading to three light active neutrino mass eigenstates, two pairs of (heavy) pseudo-Dirac mass eigenstates and one (mostly) sterile state with mass around the keV, possibly providing a dark matter candidate, and accounting for the recently observed and still unidentified monochromatic 3.5 keV line in galaxy cluster spectra. The conventional production mechanism through oscillation from active neutrinos can account only for ∼ 43% of the observed relic density. This can be slightly increased to ∼ 48% when including effects of entropy injection from the decay of light (with mass below 20 GeV) pseudo-Dirac neutrinos. The correct relic density can be achieved through freeze-in from the decay of heavy (above the Higgs mass) pseudo-Dirac neutrinos. This production is only effective for a limited range of masses, such that the decay occurs not too far from the electroweak phase transition. We thus propose a simple extension of the inverse seesaw framework, with an extra scalar singlet coupling to both the Higgs and the sterile neutrinos, which allows to achieve the correct dark matter abundance in a broader region of the parameter space, in particular in the low mass region for the pseudo-Dirac neutrinos.
Highlights
SM particle content, are very attractive scenarios
In order to properly take into account the possibility of only a partial contribution of the sterile neutrinos to the total DM abundance, we have adopted the results presented in [32] where the Lyman-α data have been considered in the case in which sterile neutrinos WDM account for the total DM abundance, as well as in the case in which they contribute only to a fraction
In this study we have considered the possibility of simultaneously addressing the dark matter problem and the neutrino mass generation mechanism
Summary
The inverse seesaw mechanism can be embedded into the framework of the SM by introducing a mass term for neutrinos of the form:. The most peculiar signatures of the ISS scenario are, as a consequence of the large Yukawa couplings of the right-handed neutrinos, additional decay channels of the Higgs boson into a heavy and an ordinary neutrino, if kinematically allowed, or into three SM fermions through an off-shell neutrino. These decay modes can be searched both directly, in particular the ones with leptonic final states [21, 22], and indirectly, in global fits of the Higgs data, by looking at deviations from the SM prediction in the branching ratios of the observed channels [21]. We remark that a sensitive improvement of these constraints in the low mass region is expected from the recently proposed SHIP [26]
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