Abstract
We analyze a low energy effective model of Dark Matter in which the thermal relic density is provided by a singlet Majorana fermion which interacts with the Higgs fields via higher dimensional operators. Direct detection signatures may be reduced if blind spot solutions exist, which naturally appear in models with extended Higgs sectors. Explicit mass terms for the Majorana fermion can be forbidden by a Z3 symmetry, which in addition leads to a reduction of the number of higher dimensional operators. Moreover, a weak scale mass for the Majorana fermion is naturally obtained from the vacuum expectation value of a scalar singlet field. The proper relic density may be obtained by the s-channel interchange of Higgs and gauge bosons, with the longitudinal mode of the Z boson (the neutral Goldstone mode) playing a relevant role in the annihilation process. This model shares many properties with the Next-to-Minimal Supersymmetric extension of the Standard Model (NMSSM) with light singlinos and heavy scalar and gauge superpartners. In order to test the validity of the low energy effective field theory, we compare its predictions with those of the ultraviolet complete NMSSM. Extending our framework to include Z3 neutral Majorana fermions, analogous to the bino in the NMSSM, we find the appearance of a new bino-singlino well tempered Dark Matter region.
Highlights
Current bounds from direct detection experiments [1,2,3,4,5,6] have set stringent limits on weakly interacting massive particle (WIMP) DM scenarios where the relic density proceeds from thermal production mediated by Higgs and gauge bosons
We explore an EFT describing the interactions of Majorana fermion WIMPs with an extended Higgs sector, comprised of a type II 2HDM and a SM gauge singlet
We assume that all explicit mass terms are forbidden, which may be realized by imposing a Z3 symmetry
Summary
As motivated in the introduction, we will consider a model of SM singlet Majorana fermion DM, which has no renormalizable interactions with SM particles. That if dealing with on-shell χ fields, there is a redundancy in the above terms, since the application of the equation of motion on the terms proportional to the derivative of χ will lead to terms proportional to the χ mass, which appear from the κ-term when inserting the vev of the field S Another important point to note from eq (2.13) is that the presence of derivative terms allows for interactions between the Goldstone G0 and DM, absent in eq (2.11), which as we shall see turn out to be relevant for the thermal annihilation cross section. That the direct expansion of the derivative terms proportional to α in eq (2.13) leads to interactions with the CP-even Higgs bosons when the derivative is acting on the Majorana fermion fields, and to derivative interactions with the CP-odd Higgs states when the derivative is acting on the Higgs doublets, as required by hermiticity. The interactions of the CP-odd singlet state AS are analogous to its CP-even counterpart,
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