Abstract
The Higgs portal to scalar Dark Matter is considered in the context of non-linearly realised electroweak symmetry breaking. We determine the dominant interactions of gauge bosons and the physical Higgs particle $h$ to a scalar singlet dark matter candidate. Phenomenological consequences are also studied in detail, including the possibility of distinguishing this scenario from the standard Higgs portal in which the electroweak symmetry breaking is linearly realised. Two features of significant impact are: i) the connection between the electroweak scale $v$ and the Higgs particle departs from the $(v+h)$ functional dependence, as the Higgs field is not necessarily an exact electroweak doublet; ii) the presence of specific couplings that arise at different order in the non-linear and in the linear expansions. These facts deeply affect the dark matter relic abundance, as well as the expected signals in direct and indirect searches and collider phenomenology, where Dark Matter production rates are enhanced with respect to the standard portal.
Highlights
Assuming, as customary, a discrete Z2 symmetry [5, 6] — under which the DM singlet scalar candidate S is odd and the SM fields are even to ensure DM stability — the HiggsDM portal takes the form λSS2Φ†Φ −→ λSS2(v + h)2 −→ λSS2(2vh + h2)
The Higgs portal to scalar Dark Matter is considered in the context of nonlinearly realised electroweak symmetry breaking
We determine the dominant interactions of gauge bosons and the physical Higgs particle h to a scalar singlet Dark Matter candidate
Summary
We restrict the analysis to the purely bosonic sector, except for the fermionic Yukawa-like terms. Would ΛDM coincide with Λs or f , it would indicate a common origin for the Higgs and the DM candidate, as it occurs in models where both have their origin as Goldstone bosons of the high-energy strong dynamics [54,55,56] Notice that, in such a scenario, the behavior of the S field is expected to follow closely that of the Higgs particle: its dependence should be encoded in generic functions F (S) invariant under the. In eq (2.2), the right-handed fermions have been gathered in SU(2)R quark and lepton doublets, QR ≡ {uR, dR} and LR ≡ {νR, eR}, while the Yukawa couplings are encoded in YQ ≡ diag{YU , YD} and YL ≡ diag{Yν , Y }, i.e. it assumes Higgs couplings aligned with fermion masses This Lagrangian is akin to the SM one written in chiral notation, but for the presence of the F (h) functions and the custodial breaking cT term, which is strongly constrained by data.
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