Improved bounds on ℤ3 singlet dark matter

Abstract

We reconsider complex scalar singlet dark matter stabilised by a Z 3 symmetry. We refine the stability bounds on the potential and use constraints from unitarity on scattering at finite energy to place a stronger lower limit on the direct detection cross section. In addition, we improve the treatment of the thermal freeze-out by including the evolution of the dark matter temperature and its feedback onto relic abundance. In the regions where the freeze-out is dominated by resonant or semi-annihilation, the dark matter decouples kinetically from the plasma very early, around the onset of the chemical decoupling. This results in a modification of the required coupling to the Higgs, which turns out to be at most few per cent in the semi-annihilation region, thus giving credence to the standard approach to the relic density calculation in this regime. In contrast, for dark matter mass just below the Higgs resonance, the modification of the Higgs invisible width and direct and indirect detection signals can be up to a factor 6.7. The model is then currently allowed at 56.8 GeV to 58.4 GeV (depending on the details of early kinetic decoupling) M S 62.8 GeV and at M S 122 GeV if the freeze-out is dominated by semi-annihilation. We show that the whole large semi-annihilation region will be probed by the near-future measurements at the XENONnT experiment.

Asymmetric dark matter from semi-annihilation

“…For earlier studies involving different aspects of Z 3 symmetric DM, see, for example, refs. [44][45][46][47][48][49][50]. The effective low-energy interaction Lagrangian involving the χ and the φ particles is given by…”

Dark matter freeze-in from semi-production

“…This has been done recently in the context of DM freeze-out in [31,32], where it has been also shown that solving the system of equations for coupled 0-th and 2-nd moment (cBE) of (4.1) instead often gives from fairly to very good estimate of the resulting relic density. 4 At the same time the structure of the semi-annihilation and semi-production rates is technically more challenging due to the necessity of performing thermal averages on pairs of particles with different temperatures [14,15,33]. Having all this in mind we therefore leave full numerical solution of (4.1) to future work, while here we focus on the system of cBE.…”

Gravitational wave signals of pseudo-Goldstone dark matter in the Z3 complex singlet model

“…Note that the BR inv can exclude points with m χ > m h /2, because the Higgs boson can decay invisibly also to two h 2 if it is light enough. Early kinetic decoupling [92,93] may additionally enhance BR inv several times [31], but in practice this would not change the parameter space of GW signals. In particular, all our points with a potentially measurable GW signal have m χ , m 2 > m h /2.…”

“…The cubic coupling can contribute to 3 → 2 scattering for Z 3 strongly interacting (SIMP) DM [27][28][29][30]. The effects of early kinetic decoupling were studied in [31]. The Z 3 symmetry has been considered as the remnant of a dark U (1) local [32][33][34] or global [35] symmetry.…”